Graves' disease (GD) has been reported to be frequently complicated with other autoimmune diseases. However, it is rarely complicated with scleroderma-polymyositis overlap syndrome. Recently, we encountered a 35-year-old woman who developed GD and immune thrombocytopenic purpura during follow-up observation of scleroderma-dermatomyositis overlap syndrome. Platelet counts recovered after high-dose gamma-globulin therapy and bolus methylprednisolone therapy. The present case is the first report of a combination of scleroderma, dermatomyositis, GD, and immune thrombocytopenic purpura. The patient was anti-Ku antibody-positive and had relatively low natural killer T cell counts, both of which might contribute to the complication of multiple autoimmune diseases.