Aortic dissection is a life-threatening condition which is difficult to diagnose because of its variable clinical presentation and diverse pathophysiologic manifestations. We present a case in which intramural hematoma of the thoracic aorta occurred in the absence of an intimal flap. Computed tomography and magnetic resonance imaging both showed hemorrhage in the wall of the aorta. Transesophageal echocardiography also revealed a penetrating atherosclerotic ulcer in the transverse aorta as a cause of the hematoma. A high index of clinical suspicion and a combination of diagnostic procedures resulted in proper diagnosis and successful surgical treatment.