Biogen Idec Names Brian S. Posner to Board of Directors

Biogen Idec Inc. (NASDAQ: BIIB), a global biotechnology leader in the discovery, development, manufacturing and commercialization of innovative therapies, today announced the appointment of Brian S. Posner to its Board of Directors, increasing the Board to 13 members. Mr. Posner, a private investor, served as Chief Executive Officer and co–Chief Investment Officer of ClearBridge Advisors LLC from 2005 until March 2008. ClearBridge, a wholly owned subsidiary of Legg Mason Inc., is an asset management company based in New York with approximately $90 billion in assets.

"Brian Posner adds enormous Wall Street experience to our Board," said Bruce R. Ross, Chairman of Biogen Idec. "With his professional investor´s perspective, he can make important contributions to Biogen Idec as we look forward to continuing to deliver strong performance and generate value for our stockholders."

Mr. Posner, 46, served as a Portfolio Manager and an Analyst at Fidelity Investments from 1987 to 1996 and, from 1997 to 1999, at Warburg Pincus Asset Management/Credit Suisse Asset Management. In 2000, he co–founded Hygrove Partners LLC, a hedge fund, and served as the Managing Partner until joining ClearBridge in 2005.

Mr. Posner holds an undergraduate degree in history from Northwestern University and an M.B.A. in finance from the University of Chicago Graduate School of Business.

About Biogen Idec

Biogen Idec creates new standards of care in therapeutic areas with high unmet medical needs. Founded in 1978, Biogen Idec is a global leader in the discovery, development, manufacturing and commercialization of innovative therapies. Patients in more than 90 countries benefit from Biogen Idec´s significant products that address diseases such as lymphoma, multiple sclerosis and rheumatoid arthritis. For product labeling, press releases and additional information about the company, please visit www.biogenidec.com.