FILED PURSUANT TO RULE 424(B)(3)
                                                      REGISTRATION NO. 333-55386

                                  $850,000,000

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

                   PROSPECTUS SUPPLEMENT DATED MARCH 26, 2003
                      TO PROSPECTUS DATED FEBRUARY 26, 2001

      The selling securityholders table on page 30 of the prospectus is hereby
further amended to update the information to include the following entity as a
selling securityholder in the prospectus and to list its total amount of Liquid
Yield Option(TM) Notes due 2031:



                                                     AGGREGATE
                                                  PRINCIPAL AMOUNT                           COMMON            COMMON
                                                    OF NOTES AT         PERCENTAGE           STOCK             STOCK
                                                   MATURITY THAT         OF NOTES        OWNED PRIOR TO      REGISTERED
NAME                                                MAY BE SOLD         OUTSTANDING        CONVERSION         HEREBY(1)
----                                              ----------------      -----------      --------------      ----------
                                                                                                   
Conseco Annuity Assurance -
  Multi Bucket Annuity Convertible Bond Fund         $4,000,000             *                 --               36,360


* Less than 1%

----------
(1)   Assumes conversion of all 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 notes
      may increase or decrease in the future.

      The preceding table has been prepared based upon information furnished to
us by the selling securityholder named in the table. From time to time,
additional information concerning ownership of the notes and common stock may be
known by certain holders thereof not named in the preceding table, with whom we
believe we have no affiliation. Information about the selling securityholder
may change over time. Any changed information will be set forth in supplements
of amendments to this prospectus.