Alemtuzumab is a selective humanized monoclonal antibody directed against the CD52 antigen, and has been found to be a powerful treatment for relapsing remitting multiple sclerosis. Alemtuzumab demonstrated high efficacy in several clinical studies. The risk of relapse and sustained accumulation of disability showed significant reduction in the Phase II CAMMS223 and the Phase III clinical trials CARE MS I and CARE MS II. The data presented at the 32nd Congress of the European Committee for Treatment and Research in Multiple Sclerosis confirmed these results. After completion of a 1-year treatment cycle, alemtuzumab showed a sustained effect. Although the efficacy of alemtuzumab has been widely proven, several severe adverse effects have been reported with its use. Infusion-associated reactions, increased risk of infections, and secondary autoimmunity have been associated with alemtuzumab. Autoimmune disease – mainly of the thyroid – has been reported. Immune thrombocytopenic purpura and autoimmune nephropathies have been observed less frequently. These adverse effects, given the short period of alemtuzumab marketing for relapsing remitting multiple sclerosis, require strict monitoring.