A chronic traumatic thoracic aortic aneurysm, 19 years after a traffic accident was successfully treated. A 34-year-old man was admitted because of chest discomfort. An upper GI examination was performed and an esophageal submembranous tumor was suspected. However, a chest CT examination showed a thoracic descending aortic aneurysm, the maximum size of which was 7.5cm×5.5cm. The final diagnosis was chronic traumatic thoracic aortic aneurysm. Generally most cases of chronic traumatic thoracic aortic aneurysm have no symptoms for a long time after an accident. However, some have reported that the development of an aneurysm is due to not receiving treatment. We performed graft replacement using the temporary bypass method because it was an easy technique and required less heparinization. Chronic thoracic aortic aneurysms have lower risk of bleeding during the operation than acute cases. For chronic cases which have stable hemodynamics, adjunctive methods (e. g., partial extracorporeal bypass, left ventricular bypass and temporary bypass) may facilitate a safe operation.