Acute dissecting aortic aneurysm continues to be associated with a poor prognosis. Angiographic study of aortic dissecting aneurysms is useful both in establishment of the diagnosis and in delineation of anatomic details important in management. Aortography may be performed either by percutaneous Seldinger approach or through a brachial arteriotomy. The importance of verifying the position of the catheter in the false or true channel, before injecting the contrast medium under high pressure, is emphasized. Demonstration of the intimal tears, the extension of the dissection, the deformation of the true channel, the degree of aortic insufficiency and the degree of involvement of the aortic branches are the major goals of the angiographic examination. The pitfalls in angiographic diagnosis, particularly in cases with cystic medial necrosis with dissection, are discussed.