Aneurysm of the thoracic aorta may follow severe, nonpenetrating injuries of the thorax unaccompanied by rib fractures. The aneurysms characteristically appear in the first portion of the descending aorta or less commonly in the proximal ascending portion. A large aneurysm, progressive enlargement, or symptoms may necessitate excision or repair. Such repair is now feasible. Traumatic aortic aneurysm should be considered in the differential diagnosis of obscure lesions in the thorax when there is a history of severe antecedent trauma.