Exhibit 99

Media Contact:

Amanda Brown Galgay

Senior Manager, Public Affairs

Biogen Idec

Tel: (781) 464-3260

Investment Community Contact:

Ben Strain

Senior Manager, Investor Relations

Biogen Idec

Tel: (781) 464-2442

Biogen Idec Increases Revenue 6 percent to $1.4 Billion in the Third Quarter

— Non-GAAP Diluted EPS Rises 19%; GAAP Diluted EPS Up 17% —

— Long-lasting Factor IX Hemophilia Candidate Reaches Primary Safety and Efficacy Endpoints in Phase 3 Trial —

— Focus Remains on Commercial Execution, Investing in Future Success, Preparing for Upcoming Milestones —

Weston, Mass., October 25, 2012 — Biogen Idec Inc. (NASDAQ: BIIB) today announced third quarter 2012 financial results, delivering revenue growth of 6 percent to $1.4 billion and non-GAAP diluted Earnings Per Share (EPS) growth of 19 percent.

Third Quarter 2012 Highlights:

As of September 30, 2012, Biogen Idec had cash, cash equivalents and marketable securities of approximately $3.3 billion.

“Through the first three quarters of 2012, Biogen Idec is on track to accomplish what we set out to do at the beginning of the year,” said George A. Scangos, Ph.D., chief executive officer. “We have enhanced our leadership position in the multiple sclerosis market with strong results from AVONEX and TYSABRI; we have advanced our late-stage pipeline, with positive results from the registrational study for factor IX in hemophilia B; and we continue preparations for the potential launch of BG-12 next year. We look forward to data readouts for factor VIII in hemophilia A soon, followed by dexpramipexole in ALS and PEGylated interferon in relapsing MS in the coming months. Our hard work is reflected in this quarter’s results.”

TYSABRI Patient Growth

Based upon data available to us through the TOUCH^® prescribing program and other third party sources, as of the end of September 2012, we estimate that approximately 71,100 patients are on commercial and clinical TYSABRI therapy worldwide, and that cumulatively, approximately 108,300 patients have been treated with TYSABRI in the post-marketing setting.

Other Products and Royalty Revenues

Revenues from other products in the third quarter of 2012 were $28 million, compared to $17 million in the third quarter of 2011.

Table 4 provides individual product revenues.

Royalty revenues were $47 million in the third quarter of 2012, compared to $52 million in the third quarter of 2011.

For the third quarter of 2012, corporate partner revenues were $12 million, compared to $16 million in the third quarter of 2011.

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Updated 2012 Financial Guidance

Biogen Idec also updated 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.

Recent Events

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Third Quarter Events

Conference Call and Webcast

The company’s earnings conference call for the third quarter will be broadcast via the internet at 8:00 a.m. ET on October 25, 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 conference call and will be subsequently available on the website 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.

About AVONEX

AVONEX is one of the most prescribed treatments for relapsing forms of MS worldwide. AVONEX is indicated for the treatment of patients with relapsing forms of MS to slow the accumulation of physical disability and decrease the frequency of clinical exacerbations. Patients with MS in whom efficacy has been demonstrated include patients who have experienced a first clinical episode and have MRI features consistent with MS.

Symptoms of depression, suicidal ideation, or psychosis, and cases of suicide, have been reported with increased frequency with patients receiving AVONEX. Severe hepatic injury, including cases of hepatic failure has been reported rarely in patients. Rare cases of anaphylaxis have been reported. While beta interferons do not have any known direct cardiac toxicity, cases of congestive heart failure, cardiomyopathy, and cardiomyopathy with congestive heart failure have been reported in patients without known predisposition. Decreased peripheral blood counts have been reported from postmarketing experience. Seizures have been reported in patients using AVONEX, including patients with no prior history of seizure. Autoimmune disorders of multiple target organs have been reported. Routine periodic blood chemistry, hematology, liver function, and thyroid function tests are recommended. There are no adequate and well-controlled studies in pregnant women. AVONEX should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. The most common side effects associated with AVONEX treatment are flu-like symptoms, including chills, fever, myalgia, and asthenia.

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For additional important safety information, and the complete United States full prescribing information, please visit www.AVONEX.com.

About TYSABRI

TYSABRI is approved in more than 65 countries. TYSABRI is approved in the United States as a monotherapy for relapsing forms of MS, generally for patients who have had an inadequate response to, or are unable to tolerate, an alternative MS therapy. In the European Union, it is approved for highly active relapsing-remitting MS (RRMS) in adult patients who have failed to respond to beta interferon or have rapidly evolving, severe RRMS.

TYSABRI has advanced the treatment of MS patients with its established efficacy. Data from the Phase 3 AFFIRM trial, which was published in the New England Journal of Medicine, showed that after two years, TYSABRI treatment led to a 68 percent relative reduction (p<0.001) in the annualized relapse rate when compared with placebo and reduced the relative risk of disability progression by 42-54 percent (p<0.001).

TYSABRI increases the risk of progressive multifocal leukoencephalopathy (PML), an opportunistic viral infection of the brain, which usually leads to death or severe disability. Infection by the JC virus (JCV) is required for the development of PML and patients who are anti-JCV antibody positive have a higher risk of developing PML. Factors that increase the risk of PML are presence of anti-JCV antibodies, prior immunosuppressant use, and longer TYSABRI treatment duration. Patients who have all three risk factors have the highest risk of developing PML. Other serious adverse events that have occurred in TYSABRI-treated patients include hypersensitivity reactions (e.g., anaphylaxis) and infections, including opportunistic and other atypical infections. Clinically significant liver injury has also been reported in the post-marketing setting. A list of adverse events can be found in the full TYSABRI product labeling for each country where it is approved.

TYSABRI is marketed and distributed by Biogen Idec Inc. and Elan Corporation, plc. For full prescribing information, including boxed warning and important safety information, and more information about TYSABRI, please visit www.biogenidec.com or www.elan.com.

Safe Harbor

This press release contains forward-looking statements, including statements about potential product launches, 2012 financial guidance, clinical trial readouts and regulatory submissions. These forward-looking statements may be accompanied by such words as “anticipate,” “believe,” “could,” “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.

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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, TYSABRI and RITUXAN, 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, problems with our manufacturing processes and our reliance on third parties, failure to comply with government regulation, our ability to protect our intellectual property rights and have sufficient rights to market our products together with the cost of doing so, the risks of doing business internationally, failure to execute our growth initiatives, 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, environmental risks, change of control provisions in our collaborations 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.

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. and Subsidiaries

Condensed Consolidated Statements of Income

(unaudited, in thousands, except per share amounts)

TABLE 2

Biogen Idec Inc. and Subsidiaries

Condensed Consolidated Balance Sheets

(unaudited, in thousands)

TABLE 3

Biogen Idec Inc. and Subsidiaries

Condensed Consolidated Statements of Income—Non-GAAP

(unaudited, in millions, except per share amounts)

Use of Non-GAAP Financial Measures

We supplement our consolidated financial statements presented on a GAAP basis by providing additional measures which may be considered “non-GAAP” financial measures under applicable SEC rules. We believe that the disclosure of these non-GAAP financial measures provides additional insight into the ongoing economics of our business and reflects how we manage our business internally, set operational goals and forms the basis of our management incentive programs. These non-GAAP financial measures are not in accordance with generally accepted accounting principles in the United States and should not be viewed in isolation or as a substitute for reported, or GAAP, net income attributable to Biogen Idec Inc. and diluted earnings per share.

Our “Non-GAAP net income attributable to Biogen Idec Inc.” and “Non-GAAP earnings per share—Diluted” financial measures exclude the following items from GAAP net income attributable to Biogen Idec Inc. and diluted earnings per share:

1. Purchase accounting and merger-related adjustments.

We exclude certain charges related to the 2003 merger between Biogen Inc. and Idec Pharmaceuticals, Inc., certain acquisition-related items, and certain amounts in relation to the consolidation of variable interest entities for which we are the primary beneficiary. These adjustments include charges for in-process research and development, the amortization of certain acquired intangible assets and adjustments to the fair value of our contingent consideration obligations. The exclusion of these charges provides management and investors with a supplemental measure of performance which the Company believes better reflects the underlying economics of the business.

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.

3. Other items.

We evaluate other items 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 also include an adjustment to reflect the related tax effect of all reconciling items within our reconciliation of our GAAP to Non-GAAP net income attributable to Biogen Idec Inc.

TABLE 4

Biogen Idec Inc. and Subsidiaries

Product Revenues

(unaudited, in thousands)