Alemtuzumab, an anti-CD52 monoclonal antibody, is effective in the treatment of relapsing-remitting multiple sclerosis (RRMS). Common adverse effects include the development of autoimmune diseases, and Graves' disease is one of the most frequent presentations. We report here a case of alemtuzumab-induced thyroid disease in a female patient who showed a phase of thyrotoxicosis with positive anti-thyroglobulin (anti-Tg) and anti-thyroid peroxidase (TPO) antibodies, but a negative TSH receptor antibody, spontaneously followed by hypothyroidism. The aim is to illustrate the clinical presentation, evaluation over time, and the possibility to consider a conservative management up to the spontaneous resolution of the thyrotoxicosis. All these are intended to emphasize the importance of pretreatment screening and follow-up in the management of treatment with alemtuzumab.