Spontaneous hemothorax in the left pleural space occurred suddenly in a patient with thrombotic thrombocytopenic purpura (TTP). In spite of massive blood transfusion, the hemorrhage could not be stopped. The patient suffered shock due to tension hemothorax and hypovolemia, resulting in cardiac arrest. After successful cardiopulmonary resuscitation, surgical hemostasis was performed. The main cause of the bleeding was rupture of the left intercostal vein. TTP is a severe microvascular occlusive thrombotic microangiopathy that can induce congestion, vasculitis, and ischemia. This mechanism is thought to have been involved in the rupture of the intercostal vein in the present patient.