Alemtuzumab is a humanized monoclonal antibody aimed against glycoprotein CD52, which causes the depletion (elimination) of circulating T and B cells. The recovery process for the two cell populations differs, leading to disturbances in the immune system. These changes result in a reduction in the disease activity. The efficacy of alemtuzumab has been confirmed in three clinical studies: one phase II – CAMMS223 study, and two phase III – CARE-MS I and CARE-MS II studies. They have shown the clinical effectiveness of intravenous alemtuzumab in patients with the remitting form of multiple sclerosis. Interferon beta-1a was administered subcutaneously as the comparator. CAMMS223 and CARE-MS I showed the drug to have significant impact on the decrease of the relapse rate as compared to interferon, whereas CAMMS223 and CARE-MS II showed it to slow down the increase of disability in patients. Treatment with alemtuzumab, however, has not been free of significant side effects, falling essentially into three major groups: side effects directly related to the administration of the drug, severe infections, and autoimmune disorders (idiopathic thrombocytopenic purpura, impaired thyroid function, and nephropathy). Alemtuzumab therapy can be both effective and safe, provided that an appropriate programme is maintained, aimed at monitoring the adverse events.