Twenty-six patients with suspected acute aortic dissection were investigated using computed tomography (CT) as the primary mode of investigation. The diagnosis was controlled by aortography or surgery or both. There were no false-positive or false-negative studies using CT. Aortography was performed on 19 of the 21 patients with aortic dissection and was positive in each instance. However, in two illustrated cases, CT indicated proximal or type A aortic dissection, whereas the corresponding aortograms indicated distal or type B aortic dissection. In two of the 21 acute aortic dissections, only CT was performed, and in both instances surgical confirmation was obtained. The results suggest that CT is at least as accurate as aortography in the diagnosis of acute aortic dissection.