BACKGROUND: Thrombotic thrombocytopenic purpura (TTP) in adults is usually caused by autoantibody inhibitors of ADAMTS13. Treatment with plasma exchange is often effective but does not address the underlying autoimmune process. OBJECTIVE: To report the efficacy of intensive immunosuppressive therapy in refractory TTP. DESIGN: Case report. SETTING: University medical center. PATIENT: 42-year-old woman with chronic relapsing TTP. INTERVENTION: Immunosuppression therapy with rituximab and cyclophosphamide. MEASUREMENTS: ADAMTS13 activity and inhibitors and hematologic variables for TTP. RESULTS: For 19 months, the patient had relapsing thrombotic microangiopathy despite plasma exchange; splenectomy; and therapy with vincristine, prednisone, and cyclosporine. ADAMTS13 activity was low, and tests detected an IgG inhibitor that recognized the metalloprotease domain of recombinant ADAMTS13. After treatment with rituximab and cyclophosphamide, the disease remitted, ADAMTS13 levels normalized, and the inhibitor was undetectable. The patient has required no treatment for 13 months. CONCLUSION: Intensive immunosuppressive therapy can lead to sustained clinical remission in patients with refractory autoimmune TTP.