Exhibit 99

Media Contact:

Amanda Galgay

Senior Manager, Public Affairs

Biogen Idec

Tel: (781) 464-3260

Investment Community Contact:

Kia Khaleghpour

Associate Director, Investor Relations

Biogen Idec

Tel: (781) 464-2442

Biogen Idec Surpasses $5 Billion in 2011 Annual Revenue

— Non-GAAP Diluted EPS Rises 15% and GAAP Diluted EPS Up 28% —

— Preparing for BG-12 Filing in First Half of 2012 —

— Phase III data Anticipated in 2012 for Long-Lasting Factor VIII and Factor IX in

Hemophilia and Dexpramipexole in ALS —

Weston, MA, January 31, 2012 — Biogen Idec Inc. (NASDAQ: BIIB), a global biotechnology leader in the discovery, development, manufacturing and commercialization of innovative therapies, today announced its full year and fourth quarter 2011 results.

Full Year 2011 Highlights:

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Fourth Quarter 2011 Highlights:

As of December 31, 2011, Biogen Idec had cash, cash equivalents and marketable securities of approximately $3.1 billion.

“Our success in 2011 gives us a strong position on which to build,” said George A. Scangos, Ph.D., the company’s chief executive officer. “In 2012 we will focus on the continued growth and leadership of our marketed products and the advancement of our strong pipeline. We will continue to work on risk stratification to unlock the value of TYSABRI and we plan to launch the AVONEX PEN in the US to support the continued growth of AVONEX. We are working to file BG-12 as quickly as possible, and are preparing for the potential launch of the product. We also anticipate phase III data later this year for our long-acting factor VIII and factor IX in hemophilia, and dexpramipexole in ALS, and are preparing for multiple filings and product launches where the data are

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positive. At the same time we are working to strengthen our early stage pipeline through internal research and strategic collaborations to build a foundation for growth and innovation over the long term.”

TYSABRI Patient Growth

Based upon data available to us through the TOUCH^® prescribing program and other third-party sources, as of the end of December 2011, we estimate that approximately 64,400 patients were on commercial and clinical TYSABRI therapy worldwide, and that cumulatively approximately 95,300 patients have ever been treated with TYSABRI in the post-marketing setting.

Other Products and Royalties

For the full year, revenues from other products were $70 million, an increase of 36% versus 2010. Revenues from other products in the fourth quarter of 2011 were $24 million, compared to $14 million in the fourth quarter of 2010.

Table 4 provides individual product revenues.

Royalties in 2011 increased 15% to $158 million, versus 2010. Royalties were $53 million in the fourth quarter of 2011, an increase of 16% compared to the fourth quarter of 2010.

Corporate partner revenues for the full year of 2011 were $57 million, compared to $32 million in 2010. For the fourth quarter of 2011, corporate partner revenues were $20 million, compared to $6 million in 2010.

2012 Financial Guidance

Biogen Idec also released its full year 2012 financial guidance. This guidance consists of the following components:

Biogen Idec may incur charges, realize gains or experience other events in 2012 that could cause actual results to vary from this guidance.

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Recent Events

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Conference Call and Webcast

The company’s earnings conference call for the fourth quarter will be broadcast via the internet at 8:00 a.m. ET on January 31, 2012, and will be accessible through the Investors section of Biogen Idec’s homepage, www.biogenidec.com. Supplemental information in the form of a slide presentation will also be accessible at the same location on the internet at the time of the earnings conference call and will be available there subsequently for one month.

About Biogen Idec

Through cutting-edge science and medicine, Biogen Idec discovers, develops and delivers to patients worldwide innovative therapies for the treatment of neurodegenerative diseases, hemophilia and autoimmune disorders. Founded in 1978, Biogen Idec is the world’s oldest independent biotechnology company. Patients worldwide benefit from its leading multiple sclerosis therapies, and the company generates more than $5 billion in annual revenues. For product labeling, press releases and additional information about the company, please visit www.biogenidec.com.

Safe Harbor

This press release contains forward-looking statements, including statements about the anticipated development, timing and therapeutic scope of programs in our clinical pipeline, regulatory filings, prospects for growth, potential product launches and financial guidance. These forward-looking statements may be accompanied by such words as “anticipate,” “believe,” “estimate,” “expect,” “forecast,” “intend,” “may,” “plan,” “project,” “target,” “will” and other words and terms of similar meaning. You should not place undue reliance on these statements.

These statements involve risks and uncertainties that could cause actual results to differ materially from those reflected in such statements, including our dependence on our three principal products, AVONEX, RITUXAN and TYSABRI, the importance of TYSABRI’s sales growth, uncertainty of success in commercializing other products, product competition, the occurrence of adverse safety events with our products, changes in the availability of reimbursement for our products, adverse market and economic conditions, our dependence on collaborations and other third parties over which we may not always have full control, failure to execute our growth initiatives, failure to comply with government regulation, our ability to protect our intellectual property rights, and have sufficient rights to market our products and services, and the cost of doing so, the risks of doing business internationally, problems with our manufacturing processes and our reliance on third parties, charges and other costs relating to our properties, fluctuations in our effective tax rate, our ability to attract and retain qualified personnel, product liability claims, fluctuations in our operating results, the market, interest and credit risks associated with our portfolio of marketable securities, our level of indebtedness, environmental risks, change of control provisions in our collaborations, representation of activist shareholders on our board of directors, and the other risks and uncertainties that are described in the Risk Factors section of our most recent annual or quarterly report and in other reports we have filed with the SEC.

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These statements are based on our current beliefs and expectations and speak only as of the date of this press release. We do not undertake any obligation to publicly update any forward-looking statements.

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TABLE 1

Biogen Idec Inc.

December 31, 2011

Consolidated Statements of Income

(in thousands, except per share amounts)

(unaudited)

TABLE 2

Biogen Idec Inc.

December 31, 2011

Condensed Consolidated Balance Sheets

(in thousands)

(unaudited)

TABLE 3

Biogen Idec Inc.

December 31, 2011

Condensed Consolidated Statements of Income - Non-GAAP

(in millions, except per share amounts)

(unaudited)

2012 Full Year Guidance GAAP to non-GAAP adjustments

An itemized reconciliation between projected EPS on a GAAP basis and on a non-GAAP basis is as follows:

Use of Non-GAAP Financial Measures

Our “non-GAAP net income attributable to Biogen Idec Inc.” and “non-GAAP diluted EPS” financial measures exclude the following items from GAAP net income attributable to Biogen Idec Inc. and diluted EPS:

1. Purchase accounting and merger-related adjustments.

We exclude certain purchase accounting impacts, such as those related to the 2003 merger between Biogen, Inc. and Idec Pharmaceuticals, Inc., the acquisitions of Fumapharm AG, Conforma Therapeutics, Syntonix Pharmaceuticals, and Panima Pharmaceuticals AG and the consolidation of Knopp and Cardiokine. These include charges for in-process research and development and amortization of the acquired intangible assets. Excluding these charges provides management and investors with a supplemental measure of performance in which the Company’s acquired intellectual property is treated in a comparable manner to its internally developed intellectual property.

2. Stock option expense recorded in accordance with the accounting standard for share-based payments.

We believe that excluding the impact of expensing stock options better reflects the recurring economic characteristics of our business. We exclude stock option expense from our non-GAAP R&D expenses and SG&A expenses, but include the impact of all other share-based awards and cash incentives in our non-GAAP results.

3. Other items.

We evaluate these on an individual basis, and consider both the quantitative and qualitative aspects of the item, including (i) its size and nature, (ii) whether or not it relates to our ongoing business operations, and (iii) whether or not we expect it to occur as part of our normal business on a regular basis.

We believe it is important to share these non-GAAP financial measures with shareholders as they better represent the ongoing economics of the business, reflect how we manage the business internally and set operational goals, and form the basis of our management incentive programs. Non-GAAP net income attributable to Biogen Idec Inc. and diluted EPS should not be viewed in isolation or as a substitute for reported, or GAAP, net income attributable to Biogen Idec Inc. and diluted EPS.

TABLE 4

Biogen Idec Inc.

December 31, 2011

Product Revenues

(in thousands)

(unaudited)