To evaluate treatment tolerability, adherence and quality of life (QoL) over 1 year in MS (Multiple Sclerosis) participants who have been switched - due to persistent tolerability issues, particularly injection problems - from a subcutaneous injectable disease-modifying treatment (DMT) given several times a week (Rebif, Betaferon or Copaxone) to once weekly Avonex 30 μg given intra-muscularly. Avonex will be applied by the injection device Avonex Pen.

Key Inclusion Criteria:

• Continuous treatment with Rebif, Betaferon or Copaxone over at least the past year.
• Injections site tolerability issues documented in medical records or by a nurse at inclusion.
• Clinically stable (free from relapses and 6-month confirmed disability progression for at least 6 months) while on therapy.
• Documented neurological history at least for the year prior to study entry.
• Qualification for Avonex® (Avonex Pen) according to the approved indication (Clinical Isolated Syndrome) or Relapsing Remitting Multiple Sclerosis (RRMS).
• Acceptance of magnetic resonance imaging.

Key Exclusion Criteria:

• Patients who have previously entered this study.
• Treatment with Avonex during the 12 months prior to the study.
• One or more relapses and/or 6-month confirmed disability progression during the 6 months prior to the study.
• Patient on Betaferon with Neutralizing Antibodies (NAbs) more than 400 TRU (tenfold reduction units) and patients on Rebif with NAbs with more than 100 TRU.
• Secondary progressive multiple sclerosis.
• Primary progressive multiple sclerosis.
• Pregnancy or breast feeding.
• History of severe depression or attempted suicide or current suicidal ideation.
• Medical or psychiatric conditions that compromise the ability to give informed consent, to comply with the protocol, or to complete the study.
• Uncontrolled seizure disorder.
• Myopathy or clinically significant liver disease.
• Inability, in the opinion of the principal investigator or staff, to comply with protocol requirements for the duration of the study.
• Known hypersensitivity to interferon-beta or other human proteins including albumin.
• A history of drug abuse in the 6 months prior to screening.
• Treatment with any of the following in the 30 days before day 1: systemic corticosteroids, ACTH, or other investigational drugs.
• Participation in any other study involving investigational or marketed products, concomitantly or within 30 days prior to entry in the study.
• Likelihood of requiring treatment during the study period with drugs not permitted by the study protocol.

NOTE: Other protocol-defined inclusion/exclusion criteria may apply.

Recruitment by participating clinicians in Switzerland and Czech Republic.