Alemtuzumab is a highly effective treatment of relapsing-remitting multiple sclerosis (RRMS) with a complex safety profile, including secondary autoimmunity in 40% of patients [1]. We report two cases of hemophagocytic lymphohistiocytosis (HLH) in patients after alemtuzumab treatment of RRMS. This hyperinflammatory syndrome consists of fever, lymphadenopathy, pancytopenia, liver abnormalities, hyperferritinemia, raised soluble interleukin 2 (IL2) receptor and hemophagocytosis; it may be secondary to malignancies, autoimmune diseases, or infections [2]. Table 1 summarizes the diagnostic criteria for secondary HLH
