We report four male patients (from 18 to 36 years in age) with acute traumatic rupture of the aortic isthmus due to blunt chest trauma caused by motor vehicle accident in three patients and a full in one patient. Of these patients, 3 underwent segmental replacements of the descending thoracic aorta with vascular prosthesis using cardiopulmonary bypass, and an additional patient underwent the same procedure using left heart bypass. All patients survived without the development of any serious complications. Since traumatic rupture of the thoracic aorta due to blunt trauma frequently occurs in the relatively young, some form of assisted circulation is necessary to prevent the ischemic spinal cord injury from cross clamping of the aorta during repair of the rupture. We prefer cardiopulmonary bypass as a most appropriate support in emergency situations, because extensive mediastinal hematoma or sudden hemorrhage could make dissection extremely hazardous without it. However, cardiopulmonary bypass requires systemic heparinization, which predisposes the patients with associated multiple injuries to a tendency of bleeding. Thus, a thorough investigation of the preoperative status, including the severity of multiple injuries, should be undertaken, and appropriate therapeutic measures instituted before the start of cardiopulmonary bypass. The determination of the timing of operation is crucial to success in the treatment of acute traumatic ruptures of the thoracic aorta.