EXHIBIT 99.1

                    CERTIFICATION OF CHIEF EXECUTIVE OFFICER


                            CERTIFICATION PURSUANT TO


                             18 U.S.C. SECTION 1350,


                             AS ADOPTED PURSUANT TO


                  SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002




      In connection with the Quarterly Report of Automatic Data Processing, Inc.
(the "Company") on Form 10-Q for the period ending December 31, 2002 as filed
with the Securities and Exchange Commission on the date hereof (the "Report"),
I, Arthur F. Weinbach, Chief Executive Officer of the Company, certify, pursuant
to 18 U.S.C. ss. 1350, as adopted pursuant to ss. 906 of the Sarbanes-Oxley Act
of 2002, that:


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


           (2) The information contained in the Report fairly presents, in all
      material respects, the financial condition and result of operations of the
      Company.




/s/ Arthur F. Weinbach
----------------------
Arthur F. Weinbach
Chief Executive Officer
January 31, 2003