PURPOSE: To compare the clinical and radiological features of aortic intramural hematoma(IMH) to those of acute aortic dissection(AD). MATERIALS AND METHODS: We analyzed the clinical and radiological features of 12patients with aortic IMH and 43 patients with acute AD. In aortic IMH, the diagnoses were made by means of both CTand transesophageal echocardiography (TEE) and included two surgically proven cases. In acute AD, the diagnoses were made by means of CT and TEE and included 21 surgically proven cases. We com- pared patients ages, etiologies, the extent of the disease, the presence or absence of aortic branch involvement, complications, and outcomes. RESULTS: Aortic IMH tended to develop in older patients (67.8±7.9 vs. 50.4± 13.4, P<.0001) more often than acute AD. In aortic IMH, all patients had a history of hypertension ; in acute AD, hypertension occurred in 37, Marfans syndrome in three, and trauma in one. In aortic IMH, Stanford type A and B lesions were found in four patients (33%) and eight (67%), respectively. In acute AD, Stanford type A and B lesions were seen in 22 (51%) and21 (49%), respectively (p>.05). In aortic IMH, there was no involvement of aortic branches, whereas in acute AD, 14 (33%) patients showed involvement of one or more aortic branches. Complications of aortic IMH included pericardial effusion (n=2) and pleural effusion (n=4) ; in acute AD, pericardial effusion (n=7), pleural effusion(n=4), aortic insufficiency (n=8), cerebral infarction (n=3), renal infarction (n=4) and spinal infarction (n=1)were seen. There was one (8%) death due to aortic IMH and ten (23%) deaths due to acute AD (p<.01). CONCLUSION: Aortic IMH is characterized by its occurrence in older patients with hypertension, a less frequent incidence of complications, and a more favorable outcome than acute AD.