A 71-year-old woman complained of gingival bleeding and epistaxis, and was given a diagnosis of idiopathic thrombocytopenic purpura. She was successfully treated with orally administered prednisolone and azathioprine. She experienced a relapse when she was 77 years old, and immunosuppressive therapy was not effective. Platelet transfusion was performed. She died because of massive gastrointestinal bleeding. An infarct was found in the left anterior part of the myocardium at autopsy. Disseminated intravascular coagulation was not detected on pathological investigation. Abnormal platelet aggregation may be important in the pathogenesis of thrombotic disease in thrombocytopenia.