Biogen (BIIB) S-8 Registration of securities for employees

EXHIBIT 23.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We hereby consent to the incorporation by reference in this Registration Statement on Form S-8 of our report dated February 21, 2007 relating to the financial statements, management’s assessment of the effectiveness of internal control over financial reporting and the effectiveness of internal control over financial reporting, which appears in Biogen Idec Inc.’s Annual Report on Form 10-K for the year ended December 31, 2006.

/s/ PricewaterhouseCoopers LLP

Boston, Massachusetts
February 21, 2007