12 Patients with thoracic aortic aneurysm were operated between May 1985 to Sept. 1987 at the our department, Hanyang University Hospital. We retrospectively evaluated the surgical results and considered diagnosis, surgical approach and perioperative problems of thoracic aortic aneurysm. There are 9 males and 3 females in the patients. The age ranged from 23 to 61 years with the mean age at 40.6 years. The cause of the aneurysm was atherosclerosis in 5, Marfan`s syndrome in 4, syphilis In 1, trauma in 1 and annuloaortic ectasia in 1 case. According to DeBakey`s classification, Type I was 1 case, Type II was 5 cases and Type III was 6 cases. Among 6 patients with ascending aortic aneurysm, Bentall`s operation in 4 cases and ascending aorta reconstruction using to Dacron Tube Graft in 2 cases were performed successfully. 6 cases with descending aortic aneurysm were managed by prosthetic graft replacement. Chylothorax was observed in 1 patient and postoperative hemorrhage necessitating reopening of the chest occurred in 4 of operative survivors. There were 2 hospital deaths; one patient was dead during the operation and one patient was dead during the post-operative course due to low cardiac output syndrome