Chronic traumatic thoracic aneurysm which had passed over eighteen years since injury was reported. A 41-year-old man, who was involved in automobile accident 18 years before, complained back pain and was referred to our hospital for an aneurysm at the aortic isthmus. According to his history of trauma and location of aneurysm, it was diagnosed as chronic traumatic thoracic aneurysm. Graft replacement was performed under the left heart bypass by using the BioMedicus centrifugal pump. He has been doing well after the operation.