Sixty-seven patients subjected to this study composed of 32 patients treated surgically, 15 patients treated medically and 20 patients examined by autopsy for the past 8 years. Out of 32 surgical cases, 16 were operated on in an acute stage, within 2 weeks after onset and 9 out of these 16 acute cases belonged to DeBakey type I or II and 11 out of 15 autopsy cases belonged to type I or II either. Contrarily most of the medical cases were type III. Both causes of death in the acute autopsy group and operative indications in the acute surgical group were cardiac tamponade, heart failure due to aortic insufficiency, myocardial infarction and aortic rupture. Operative mortality rate was 12.5% in the acute cases and 19% in the chronic cases, late mortality rate was 19% in the acute cases and 0% in the chronic cases. Two cases of operative death had massive bleeding due to aortic rupture and massive myocardial infarction. These were the most dangerous complications of acute aortic dissections. We conclude that all patients with type I or II dissections should be operated on before fatal complications occur.