EXHIBIT 23 Consent of Independent Registered Public Accounting Firm
We consent to the incorporation by reference in the Registration Statement (Form S-8 No.
333-84055) pertaining to the Paychex, Inc. 401(k) Incentive Retirement Plan of our report dated
June 16, 2009, with respect to the financial statements and schedule of Paychex, Inc. 401(k)
Incentive Retirement Plan included in this Annual Report (Form 11-K) for the year ended December
31, 2008.
/s/ Ernst & Young LLP
June 23, 2009
Cleveland, Ohio
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