Thrombotic thrombocytopenic purpura (TTP) is a rare medical condition characterized by thrombocytopenia, microangiopathic hemolytic anemia, neurologic manifestations, and infrequently, renal involvement. In many cases, TTP is associated with deficiency of the von Willebrand factor-cleaving protease, ADAMTS13, and treatment with plasma exchange is effective in the majority of patients. We report a patient with acute TTP in whom remission was not achieved by initial treatment consisting of plasma exchange and corticosteroids. In view of the severe autoantibody-mediated ADAMTS-13 deficiency, treatment was initiated with rituximab, a chimeric monoclonal antibody directed against the CD 20 antigen present on B lymphocytes. The patient received 4 weekly infusions of rituximab (375 mg/m²). Four weeks after the last infusion of rituximab, a complete clinical and laboratory remission was documented. We conclude that rituximab should be considered in patients with TTP with acquired ADAMTS-13 deficiency, who fail to respond to standard treatment with plasma exchange and corticosteroids. Rituximab may result in a lowered requirement for plasmapheresis and avoid the complications of salvage immunosuppressive therapy.