A patient presented to our emergency department from another hospital diagnosed with pelvic fracture after a motor vehicle accident. In the ensuing 12 hours, chest pain developed, and a widened mediastinum on chest radiography was found. Posterior aortography showed aortic arch rupture. During surgery, we found a complete circumferential disruption of the arch between the brachiocephalic trunk and the carotid artery. Even though thoracic aortic injuries rarely occur in motor vehicle accidents, thoracic arch ruptures are extremely uncommon. This injury should be suspected after high-speed motor vehicle accidents, when accompanied with chest pain or widened mediastinum.