This will be prospective, multicentre, observational study. Patients who will initiate treatment with IFNβ-1b (Betaferon) will be followed up to 6 months. Baseline visit (visit 0) i.e. treatment initiation plus four follow-up visits (visits 1-4). For each patient demographics, medical history data, safety parameters, presence of flu-like symptoms and measures to prevent or treat these symptoms will be collected.