Alemtuzumab, a humanized monoclonal antibody that targets CD52 antigens on lymphocytes and monocytes, has shown efficacy in preventing relapse in relapsing-remitting multiple sclerosis. Despite known severe (yet rare) renal side effects such as anti-glomerular basement membrane disease and membranous glomerulopathy, to our knowledge, alemtuzumab has never been documented to cause drug-induced thrombotic microangiopathy. We describe a 39-year-old woman with relapsing-remitting multiple sclerosis who developed acute kidney injury requiring renal replacement therapy after 1 dose of alemtuzumab, as well as microangiopathic hemolytic anemia and thrombocytopenia.