Aortic injury caused by penetration of a fractured rib is very rare. We present a patient with aortic injury demonstrated using serial imaging studies. A 66-year-old woman fell from a ladder and sustained multiple left-side rib fractures. There was a small left hemothorax and widened mediastinum on the initial chest roentgenogram in the emergency department. Chest computed tomography (CT) revealed a posterior segmental fracture of the sixth rib on the left side with a sharp edge penetrating into the posterior aspect of the thoracic aorta. It was initially missed. More than 1000 cc of fresh blood suddenly gushed out of the chest tube 7 hours after the traumatic event. After resuscitation, an aortogram was performed which showed blood extravasation from the thoracic aorta at the rib fracture site. Unfortunately, surgical intervention was delayed and she died. Early detection and early surgical intervention are necessary in patients with a widened mediastinum and positive results on imaging studies.