Tysabri Observational Program

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.