Since 1925, 230 cases of thrombotic thrombocytopenic purpura (TTP) have been reported. This paper reports 16 cases of TTP, 11 females and 5 males, ages 16 to 60. Three patients were pregnant; one had recently aborted. Thrombocytopenic purpura was seen in 12 cases; however, severe hemorrhage was seen in only one. One patient had a normal platelet count. Hemolytic anemia with reticulocytosis (6 to 42%) was present in all but three patients. The Coombs test was negative in ten, tested. The LE-preparation was negative in six, examined. In 15 cases, headache, confusion, visual disturbances, aphasia, hemiparesis, seizures, or coma were