Natalizumab is a humanized monoclonal antibody with a selective adhesion-molecule inhibitor effect, and a demonstrated efficacy in decreasing the frequency of relapses and progression of disability in relapsing-remitting multiple sclerosis (RR MS). After the approval of FDA and EMEA in MS cases unresponsive to immunomodulating therapy or in severe MS patients also not previously treated with interferons, and considering the concern on the possible side effects, an accurate program of surveillance was organized in our country by a combined effort of AIFA, Cineca, Department of Pharmacology of University of Bologna, and a group of neurologists appointed by the National Society of Neurology (SIN). After 15 months from the authorization of natalizumab therapy in MS, as of 31 March 2008, 908 cases have been treated with natalizumab and enrolled in this pharmaco-vigilance study. The mean age is 35 years, while the duration of disease is longer and disability is higher than that reported in the registrative study. Side effects are at the moment mild and similar to those previously described. At follow-up, the majority of treated cases are stable or ameliorated. The treatment was discontinued in 6% of patients.