The diagnosis of rupture of the thoracic aorta or its major branches depends largely on the recognition of mediastinal hemorrhage from the initial chest radiograph and subsequent thoracic aortography. This review discusses the radiographic manifestations of mediastinal hemorrhage, including widening of the mediastinum; a ratio of mediastinal width to chest width greater than 0.25; abnormalities of aortic contour; opacification of the aortopulmonary window; depression of the left main bronchus; deviation of the trachea to the right; deviation of the nasogastric tube to the right; the apical cap sign; widening of the paraspinal lines; widening of the right paratracheal stripe; and left hemothorax. The relationship of these manifestations to major thoracic arterial injury is examined. Pitfalls in the radiographic evaluation of mediastinal abnormalities are considered, and indications for computed tomography of the thorax and thoracic aortography in the severely injured patient are reviewed.