At the end of 2006 a country-based surveillance program on natalizumab therapy in multiple sclerosis was settled in Italy by a collaborative effort of the Italian Drug Agency (AIFA) and a group of experts and neurologists appointed by the National Society of Neurology (SIN). After 2 years, 1,818 patients are registered in the database. The majority of cases (88.6%) failed the therapy with beta interferon or glatiramer acetate and had relapses or accumulated disability during immunomodulating treatment, while 11.4% of patients enrolled in the surveillance study were not previously treated with immunomodulating therapies and had a rapidly evolving clinical course. Almost 10% of the patients treated with natalizumab interrupted, for various different reasons, the therapy. Treatment was well tolerated and side effects were similar to those reported in the registrative studies. The majority of treated cases are stable or ameliorated.