Thrombotic thrombocytopenic purpura (TTP) is a serious disorder of unknown etiology. Clinical findings are the result of vascular occlusions by platelet aggregates. Treatment with plasma exchange, often used in combination with corticosteroids, vincristine, aspirin, and dipyridamole, has reduced mortality to 20%. Relapses may occur even after long disease-free intervals. In this report we describe our experience with splenectomy in patients with relapsing TTP. Between July 1978 and March 1994, 16 patients with TTP were treated in our hospital. Five of the 13 patients surviving the first episode of TTP had relapses. Most relapses were treated as the first episode of TTP with plasma exchange with fresh-frozen plasma, followed by plasma infusions, corticosteroids, and vincristine. Sometimes aspirin and dipyridamole were added. Splenectomy was performed after five relapses in the first two patients and after two and three relapses in the other patients. Before splenectomy the disease-free interval varied from 3 weeks to 27 months and the incidence rate of relapses was 1.5 relapse/patient/year. None of the patients had relapses after splenectomy. The mean follow-up after splenectomy is 39 months with a range of 9-62 months. We conclude that patients with relapsing TTP can benefit from splenectomy, since it seems to increase disease-free intervals. Further investigation is necessary to understand the role of the spleen in the pathogenesis of TTP.