Moschcowitz syndrome or thrombotic thrombocytopenic purpura is a rare disorder with a poor prognosis. This syndrome is characterized by a microangiopathic hemolytic anemia with thrombocytopenia, neurologic symptoms and renal disease. The vascular lesion consists of disseminated hyaline thrombi in the microvasculature composed mainly of platelet aggregates. The mechanisms are still poorly understood and are probably multiple. Recent data focus on an abnormal endothelial synthesis of prostacyclin and the presence of a factor (or the reduction of its inhibitor) in plasma able to induce intravascular disseminated platelet aggregation. The most efficient therapy seems to be infusions of fresh plasma with or without plasma exchange.