A rare case of dermatomyositis and thrombotic thrombocytopenic purpura (TTP), which responded dramatically to high-dose gamma globulin and vincristine is presented. A 42-year old man was admitted for evaluation of polymyalgia and skin change of the face and fingers. Findings of muscle biopsy was consistent with the diagnosis of dermatomyositis. During the course of his hospital stay, he had diffuse purpura, hematuria, high fever, and his consciousness became disturbed. The hemoglobin level and the platelet count decreased. Based on microangiopathic hemolytic anemia, thrombocytopenia and neurological abnormality, a clinical diagnosis of TTP was made. Therapy included high-dose gamma globulin, vincristine, corticosteroids and dextran. One week later, his consciousness became clear, hematological findings improved, and prolonged remission has been maintained for more than 19 months at the time of this report. This case suggests that gamma globulin and vincristine are effective in some with TTP cases. Case reports that have appeared in the Japanese literature are summarized and reviewed in terms of treatment.