Missed vascular injuries following blunt traumas can lead to fatal clinical conditions that require an emergency intervention. Aortic transection (AT) is the most fatal complication of these missed vascular injuries. In this case report an AT that developed following a blunt trauma is presented. The patient was admitted with effort dyspnea and tachycardia. He had a history of blunt trauma three years ago. There was an enlargement of the upper mediastinum on X-ray studies. Thoracal magnetic resonance imaging and computed tomography revealed aneurysm of the descending aorta. Dacron graft interposition was performed as surgical treatment. The symptom and signs disappeared dramatically after the operation.