QuickLinks -- Click here to rapidly navigate through this document

Exhibit 23

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

        We hereby consent to the incorporation by reference in the Registration Statements on Form S-3 (File Nos. 33-61853, 333-51790, 333-63802, 333-100727, 333-109179) and in the Registration Statements on Form S-8 (File Nos. 33-58359, 33-60437, 333-10003, 333-33249, 333-83677, 333-51906, 33-30007, 33-68208, 333-33265, 333-10005, 333-33251, 333-83669, 333-33291, 33-21241, 333-55126, 333-42371, 333-81275, 333-87967, 333-81277, 333-83673, 333-64103, 333-83681, 333-51872, 333-52202, 333-66130, 333-70310, 333-76762, 333-76766, 333-76768, 333-76770, 333-100722, 333-90514, 333-90512, 333-90510, 333-64095, 333-106691, 333-106692, 333-111314, 333-116650, 333-116651, 333-116653, 333-114184, 333-125723, 333-125724, 333-125726, 333-139491, 333-139492, 333-143467, 333-143468, 333-143469, 333-153898) of Genzyme Corporation of our report dated February 27, 2009 relating to the financial statements and the effectiveness of internal control over financial reporting, which appears in the Annual Report to Shareholders, which is incorporated in this Annual Report on Form 10-K. We also consent to the incorporation by reference of our report dated February 27, 2009 relating to the financial statement schedule, which appears in this Form 10-K, and of our report dated February 25, 2008 relating to the financial statements of BioMarin/Genzyme LLC, which appears in this Form 10-K.

/s/ PRICEWATERHOUSECOOPERS LLP

Boston, Massachusetts
February 27, 2009

QuickLinks

Exhibit 23

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM