PROSPECTUS SUPPLEMENT
(To Prospectus Dated February 26, 2001)
                                                Filed Pursuant to Rule 424(b)(3)
                                            Registration Statement No. 333-55386

                                  $850,000,000

                               OMNICOM GROUP INC.
                      Liquid Yield Option(TM) Notes due 2031
                              (Zero Coupon-Senior)

      This  prospectus   supplement   relates  to  the  resale  by  the  selling
securityholders  of Liquid  Yield  Option(TM)  Notes (Zero Coupon -- Senior) due
2031 (the "LYONs") of Omnicom Group Inc. and the shares of common stock issuable
upon the conversion and/or redemption of the LYONs.

      This  prospectus  supplement  should  be  read  in  conjunction  with  the
prospectus  dated  February  26,  2001,  which  is to  be  delivered  with  this
prospectus  supplement.  All  capitalized  terms  used  but not  defined  in the
prospectus supplement shall have the meanings given them in the prospectus.

      The  following  information  replaces  in  its  entirety  the  information
provided in the prospectus under the caption "Selling Securityholders."

                             SELLING SECURITYHOLDERS

      The LYONs were originally issued by us and sold by Merrill Lynch,  Pierce,
Fenner & Smith  Incorporated  in a  transaction  exempt  from  the  registration
requirements  of the  Securities Act to persons  reasonably  believed by Merrill
Lynch to be "qualified  institutional buyers" (as defined by Rule 144A under the
Securities  Act).  The  selling   securityholders  (which  term  includes  their
transferees,  pledgees,  donees or  successors)  may from time to time offer and
sell pursuant to this prospectus, as amended or supplemented, any and all of the
LYONs and the shares of common stock issuable upon conversion  and/or redemption
of the LYONs.

      Set  forth  below  are the  names  of  each  selling  securityholder,  the
principal  amount of LYONs that may be offered  by such  selling  securityholder
pursuant  to this  prospectus,  as  amended or  supplemented,  and the number of
shares of common stock into which such LYONs are  convertible.  Unless set forth
below, none of the selling  securityholders has had a material relationship with
us or any of our predecessors or affiliates within the past three years.

      The following  table sets forth certain  information  received by us on or
prior to May 31, 2001.  However, any or all of the LYONs or common  stock listed
below may be  offered  for sale  pursuant  to this  prospectus,  as  amended  or
supplemented,  by the selling securityholders from time to time. Accordingly, no
estimate  can be given as to the  amounts of LYONs or common  stock that will be
held by the selling  securityholders  upon  consummation  of any such sales.  In
addition,   the  selling   securityholders   identified  below  may  have  sold,
transferred  or otherwise  disposed of all or a portion of their LYONs since the
date  on  which  the  information   regarding  their  LYONs  was  provided,   in
transactions exempt from the registration requirements of the Securities Act.



                                                                                              Common Stock
                                                     Aggregate Principal Amount  Percentage   Beneficially   Common Stock
                                                        of LYONs at Maturity      of LYONs    Owned Prior     Registered
                        Name                              that may be Sold       Outstanding  to Conversion    Hereby(1)
-------------------------------------------------    --------------------------  -----------  -------------   -----------
                                                                                                 
AAM/Zazove Institutional Income Fund L.P. (BS) ....        $  1,000,000                *           --            9,090
AFTRA Health Fund .................................             475,000                *           --            4,317
AIG SoundShore Holdings Ltd. ......................           6,451,000                *           --           58,639
AIG SoundShore Opportunity Holding Fund Ltd. ......           7,328,000                *           --           66,611
AIG SoundShore Strategic Holding Fund Ltd. ........           4,221,000                *           --           38,368
Allstate Insurance Company ........................           1,700,000                *       85,300           15,453
Allstate Life Insurance Company ...................           2,300,000                *       85,300           20,907
American Country Insurance Company ................             600,000                *           --            5,454
American Founders Life Insurance Company ..........             100,000                *           --              909
American Pioneer Life Ins. Co. of New York ........              90,000                *           --              818
American Progressive Life and Health Ins. Co. of
   New York .......................................              90,000                *           --              818
American Public Entity Excess Pool ................              60,000                *           --              545
AmWest Surety Insurance Company ...................             270,000                *           --            2,454
Arpeggio Fund, L.P. ...............................           1,000,000                *           --            9,090
Baltimore Life Insurance Company ..................             300,000                *           --            2,727
BCS Life Insurance Company ........................             650,000                *           --            5,908
Bear, Stearns & Co., Inc. .........................           2,500,000                *           --           22,725
Brown & Williamson Tobacco Master
   Retirement Trust ...............................             100,000                *           --              909
Buckeye State Mutual Insurance Company ............              30,000                *           --              272







                                                                                              Common Stock
                                                     Aggregate Principal Amount  Percentage   Beneficially   Common Stock
                                                        of LYONs at Maturity      of LYONs    Owned Prior     Registered
                        Name                              that may be Sold       Outstanding  to Conversion    Hereby(1)
-------------------------------------------------    --------------------------  -----------  -------------   -----------
                                                                                                 
Catholic Mutual Relief Society of America .........             500,000                *           --            4,545
Catholic Mutual Relief Society of America
   Retirement Plan & Trust ........................             300,000                *           --            2,727
Catholic Relief Insurance Company of America ......             600,000                *           --            5,454
Celina Mutual Insurance Company ...................              25,000                *           --              227
Central States Health & Life Company of Omaha .....             220,000                *           --            1,999
Chicago Mutual Insurance Company ..................              70,000                *           --              636
Chrysler Insurance Company ........................           4,000,000                *           --           36,360
The Class IC Company, Ltd. ........................           2,000,000                *           --           18,180
Colonial Life Insurance Company of Texas ..........              25,000                *           --              227
Commonwealth Dealers - CDLIC ......................             200,000                *           --            1,818
Concord Life Insurance Company ....................             140,000                *           --            1,272
Condor Insurance Company ..........................             180,000                *           --            1,636
Credit Suisse First Boston Corporation ............             200,000                *           --            1,818
CSA Fraternal Life Insurance Company ..............             130,000                *           --            1,181
Cumberland Mutual Fire Insurance Company ..........             220,000                *           --            1,999
Dakota Truck Underwriters .........................              25,000                *           --              227
D.E. Shaw Investments, L.P. .......................             800,000                *           --            7,272
D.E. Shaw Valence, L.P. ...........................           3,200,000                *           --           29,088
Educators Mutual Life Insurance Company ...........             250,000                *           --            2,272
Farmers Home Mutual Insurance Company .............             450,000                *           --            4,090
Federated Rural Electric Insurance Exchange .......             360,000                *           --            3,272
Fidelity Financial Trust: Fidelity Convertible
   Securities Fund ................................           6,000,000                *           --           54,540
First Dakota Indemnity Company ....................              20,000                *           --              181
First Mercury Insurance Company ...................             620,000                *           --            5,635
First Union National Bank .........................          21,000,000             2.47%          --          190,890
Forest Alternative Strategies Fund II LP A5M ......             150,000                *           --            1,363
Forest Fulcrum Fund L.P. ..........................           1,200,000                *           --           10,908
Forest Global Convertible Fund A5 .................           5,850,000                *           --           53,176
Fort Dearborn Life Insurance Company ..............             250,000                *           --            2,272
Gaia Offshore Master Fund Ltd. ....................          12,500,000             1.47%          --          113,625
GLG Global Convertible Fund .......................           1,650,000                *           --           14,998
GLG Global Convertible Ucits Fund .................             350,000                *           --            3,181
GLG Market Neutral Fund ...........................           2,500,000                *           --           22,725
Goldman Sachs and Company .........................             550,000                *           --            4,999
Goodville Mutual Casualty Company .................              50,000                *           --              454
Grain Dealers Mutual Insurance ....................             160,000                *           --            1,454
Green Tree Perpetual Assurance Company ............             300,000                *           --            2,727
Guaranty Income Life Insurance Company ............             450,000                *           --            4,090
Guarantee Trust Life Insurance Company ............           1,000,000                *           --            9,090
Hamilton Partners Limited .........................          20,000,000             2.35%          --          181,800
Hannover Life Reassurance Company of America ......             500,000                *           --            4,545
HFR Master Fund LTD ...............................             200,000                *           --            1,818
HighBridge International LLC ......................          30,000,000             3.53%          --          272,700
Holy Family Society ...............................              90,000                *           --              818
IMF Convertible Fund ..............................             700,000                *           --            6,363
Integrity Mutual Insurance Company ................             300,000                *           --            2,727
Investcorp - SAM Fund Ltd. ........................           3,200,000                *           --           29,088
ISBA Mutual Insurance Company .....................             225,000                *           --            2,045
J.P. Morgan Securities, Inc. ......................          39,000,000             4.59%          --          354,510
Kanawha Insurance Company .........................             250,000                *           --            2,272
KBC Financial Products USA ........................           2,000,000                *           --           18,180
Landmark Life Insurance Company ...................              60,000                *           --              545
Lebanon Mutual Insurance Company ..................             100,000                *           --              909
LLT Limited .......................................             400,000                *           --            3,636
Loyal Christian Benefit Association ...............              80,000                *           --              727
Lyxor Master Fund, c/o Forest Investment
   Management L.L.C ...............................           1,600,000                *           --           14,544
Mainstay Convertible Fund .........................           7,000,000                *           --           63,630
Mainstay VP Convertible Portfolio .................           1,600,000                *           --           14,544
Marquette Indemnity and Life Insurance Comp .......              80,000                *           --              727
McMahan Securities Co. L.P. .......................             100,000                *           --              909
Medico Life Insurance Company .....................             800,000                *           --            7,272
Medmare Insurance Company .........................             500,000                *           --            4,545
Merrill Lynch, Pierce, Fenner & Smith
   Incorporated(2) ................................          65,225,000             7.67%          --          592,895
Michigan Professional Insurance Exchange ..........             110,000                *           --              999
Mid America Life Insurance Company ................             100,000                *           --              909
Middle Cities Risk Management Trust ...............             200,000                *           --            1,818
Midwest Security Life .............................             280,000                *           --            2,545
Morgan Stanley & Co. Incorporated(3) ..............          15,000,000             1.76%          --          136,350
MSC Life ..........................................              50,000                *           --              454






                                                                                              Common Stock
                                                     Aggregate Principal Amount  Percentage   Beneficially   Common Stock
                                                        of LYONs at Maturity      of LYONs    Owned Prior     Registered
                        Name                              that may be Sold       Outstanding  to Conversion    Hereby(1)
-------------------------------------------------    --------------------------  -----------  -------------   -----------
                                                                                                 
Mutual Protective Insurance Company ...............           1,100,000                *           --            9,999
National Mutual Insurance Company .................              30,000                *           --            4,545
NCMIC .............................................             500,000                *           --              272
New Era Life Insurance Company ....................             300,000                *           --            2,727
New York Life Separate Account #7 .................             900,000                *           --            8,181
Nomura Securities International, Inc. .............          15,000,000             1.76%     307,158          136,350
Oak Casualty Insurance Company ....................              40,000                *           --              363
Onyx Fund Holdings, LDC ...........................          12,000,000             1.41%          --          109,080
PHICO Insurance Company ...........................             600,000                *           --            5,454
Physicians Mutual Insurance Company ...............             600,000                *           --            5,454
Pioneer Insurance Company .........................              80,000                *           --              727
Premera Blue Cross ................................           1,500,000                *           --           13,635
R2 Investments, LDC ...............................         122,000,000            14.35%          --        1,108,980
Republic Mutual Insurance Company .................              15,000                *           --              136
Rhapsody Fund, LP. ................................           3,700,000                *           --           33,633
Royal Bank of Canada ..............................           6,000,000                *       95,033           54,540
Sagamore Hill Hub Fund Ltd. .......................          14,500,000             1.71%          --          131,805
Salomon Smith Barney Inc. .........................           3,000,000                *           --           27,270
SAM Investments LDC ...............................          50,000,000             5.88%          --          454,500
San Diego County Employees Retirement Association .           2,800,000                *           --           25,452
St. Albans Partners Ltd. ..........................          13,000,000             1.53%          --          118,170
Standard Mutual Insurance Company .................             300,000                *           --            2,727
State National Insurance Company ..................             120,000                *           --            1,090
Sylvan IMA Ltd., c/o Forest Investment
   Management L.L.C ...............................             800,000                *           --            7,272
Texas Builders Insurance Company ..................             120,000                *           --            1,090
Texas Hospital Insurance Exchange .................              25,000                *           --              227
Transguard Insurance Company of America, Inc. .....             900,000                *           --            8,181
Tribeca Investments LLC ...........................          25,000,000             2.94%          --          227,250
United National Insurance Company .................             850,000                *           --            7,726
Western Home Insurance Company ....................             180,000                *           --            1,636
West Virginia Fire Insurance Company ..............              10,000                *           --               90
Westward Life Insurance Company ...................             180,000                *           --            1,636
White River Securities L.L.C ......................           2,500,000                *           --           22,725
Wisconsin Lawyers Mutual Insurance company ........             200,000                *           --            1,818
Wisconsin Mutual Insurance Company ................             140,000                *           --            1,272
World Insurance Company ...........................             250,000                *           --            2,272
All other holders of LYONs or future transferees,
   pledgees,  donees or successors of any such
   holders(4)(5) ..................................         283,250,000            46.58%          --        2,574,769
                                                           ------------           ------      -------        ---------
   Total ..........................................        $850,000,000           100.00%     572,791        7,726,500
                                                           ============           ======      =======        =========


*  Less than 1%

----------
(1)   Assumes  conversion of all of the holder's  LYONs at a conversion  rate of
      9.09 shares of common stock per $1,000 principal amount at maturity of the
      LYONs.  However,  this  conversion  rate will be subject to  adjustment as
      described  under  "Description  of the LYONs --  Conversion  Rights." As a
      result,  the amount of common stock issuable upon  conversion of the LYONs
      may increase or decrease in the future.

(2)   Merrill  Lynch,  Pierce,  Fenner  & Smith  Incorporated  was  the  initial
      purchaser in the private  placement on February 7, 2001 in which the LYONs
      were originally issued.  Merrill Lynch has advised us that it is not aware
      of any position,  office or directorship relationship that it has had with
      Omnicom or its affiliates.  However,  Merrill Lynch has advised us that it
      may have,  from time to time,  acted in a  financial  investment  advisory
      capacity to Omnicom.

(3)   Morgan  Stanley  & Co.  Incorporated  was  the  initial  purchaser  in the
      offering of $230,000,000  aggregate principal amount of 2 1/4% convertible
      subordinated debentures due 2013 on January 6, 1998 by Omnicom.

(4)   Information  about  other  selling  securityholders  will be set  forth in
      prospectus supplements, if required.

(5)   Assumes  that any other  holders  of  LYONs,  or any  future  transferees,
      pledgees, donees or successors of or from any such other holders of LYONs,
      do not  beneficially  own any common  stock  other  than the common  stock
      issuable upon conversion of the LYONs at the initial conversion rate.

      The preceding table has been prepared based upon information  furnished to
us by the  selling  securityholders  named  in the  table.  From  time to  time,
additional  information  concerning  ownership of the LYONs and common stock may
rest with certain holders thereof not named in the preceding table, with whom we
believe we have no affiliation.  Information  about the selling  securityholders
may  change  from  over  time.  Any  changed  information  will be set  forth in
prospectus supplements.
                                   ----------
             The date of this Prospectus Supplement is June 1, 2001.

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