Exhibit 32.1

                                CERTIFICATION OF
                                QUARTERLY REPORT
                                  ON FORM 10-Q

Pursuant to 18 U.S.C. ss. 1350, as adopted pursuant to ss. 906 of the
Sarbanes-Oxley Act of 2002, in connection with the filing of Omnicom Group
Inc.'s Quarterly Report on Form 10-Q for the quarter ended June 30, 2003, as
filed with the Securities and Exchange Commission on the date hereof (the
"Report"), each of the undersigned officers of Omnicom certifies, that, to such
officer's knowledge:

     o    the Report fully complies with the requirements of Section 13(a) or
          15(d) of the Securities Exchange Act of 1934; and

     o    the information contained in the Report fairly presents, in all
          material respects, the financial condition and results of operations
          of Omnicom as of the dates and for the periods expressed in the
          Report.

Executed as of August 8, 2003.


                                                /s/ John D. Wren
                               ----------------------------------------------
                               Name:  John D. Wren
                               Title: Chief Executive Officer and President



                                        /s/ Randall J. Weisenburger
                               ----------------------------------------------
                               Name: Randall J. Weisenburger
                               Title: Executive Vice President and
                                      Chief Financial Officer