The association between thrombotic thrombocytopenic purpura (TTP) and autoimmune hematological conditions is reported in 2 patients. In a 35-year-old man, acute autoimmune hemolytic anemia (AIHA) was diagnosed in 1960; until 1965 he was free of disease, when he abruptly developed TTP and failed to respond to blood transfusions and corticosteroids. In a 14-year-old girl, autoimmune thrombocytopenic purpura (AITP) was diagnosed in 1981 and treated with corticosteroids and splenectomy. Four years later the patient was admitted with acute catastrophic signs and symptoms of TTP and failed to respond to plasmapheresis and plasma transfusions. The present case reports of associations between AIHA and AITP with TTP support the connection of the latter with abnormalities of the immune system.