A comparative study was done restrospectively in 26 patients with dissecting aneurysm which was diagnosed radiologically with both CT and angiography in Department of Radioligy, Seoul National University Hospital from May 1984 to August 1987. Adventage and disadvantage of Computerized tomography were summarized after comparetive analysis of the radiological findings of the 26 cases. 1) Among the 26 patients, DeBakey type I was 8, type II was 1 and type III was 17. 2) The most frequent CT findings were linear low density due to intimal flap in the aorta in 65%(17/26), followed by findings of hemothorax in 46%(12/26) and unopacified false lumen in 38%(10/26). 3)The advantage of CT over angiography can be summarized as follows through the comparative analysis ; a. Communication of the false lumen with true lumen through opacipication of false lumen or noot. b. Extent of the dissection especially in ascending aorta and aortic arch. c. Hemothorax, hemopericardium and periaortic hematoma. d. displacement of intimal calcipication and thrombosis of the associated aneurysm. 4) The disadvantage of CT was difficulties to evaluate major branch invovement, aortic valvular insufficiency, tear site and Re-entry.