The study population includes patients with relapsing-remitting multiple sclerosis (RR-MS) being treated at least for 12 months with natalizumab and having decided to stop natalizumab treatment and to de-escalate their therapy to a first line treatment with interferon beta-1b. They will be treated during 12 months with interferon-beta 1b 250 mcg given subcutaneously every other day. A 12-month follow-up period with the same treatment is planned.