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Treatment tested

• Natalizumab

  Integrin alpha-4/beta-1 inhibitor|Integrin alpha-4/beta-7 inhibitor

Other measures (9)

Key Inclusion Criteria: * Documented diagnosis of Relapsing Remitting Multiple Sclerosis * The decision to treat with Tysabri must precede enrollment * Patient must be a new Tysabri user, and must not have had more than 3 Tysabri infusions prior to enrollment * Must have had at least one relapse in the previous year, and must satisfy locally approved therapeutic indications for Tysabri Key Exclusion Criteria: * History of Progressive Multifocal Leukoencephalopathy or other opportunistic infections, or an increased risk of opportunistic infections * History of positive anti-Tysabri antibodies * Concomitant Immunomodulatory or immunosuppressive therapy during therapy with Tysabri * Patient immunocompromised at the time of enrollment * Known active malignancy * Women must not be breast feeding or pregnant, or planning to become pregnant (must use birth control unless surgically sterile) NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.

The primary objective of this study is to assess the long-term safety and impact on disease activity and progression of Tysabri in participants with relapsing remitting multiple sclerosis (RRMS) in a clinical practice setting.