In 16 years, 33 operations were performed on 32 patients out of a total of 55 with dissecting thoracic aneurysms. The overall mortality was 64%. This was much higher (88%) for type 1 cases (tear near the aortic valve and dissection extending beyond the descending aorta) than for type 2 (tear and dissection confined to ascending aorta) or for type 3 (tear and dissection distal to left subclavian) in which the mortality was 40% and 44%, respectively. At all levels, the mortality was higher for acute than for chronic dissections. Since, it is essential that the torn segment of the aorta be removed for a successful operation, precise aortography is a preoperative requirement. In most instances surgical therapy is indicated and these indications are defined.