Two patients with dissecting aneurysms of the aorta of Debakey type I and II, 10 healthy subjects, and 2 patients with signs mimicking aortic-root dissection were studied by two-dimensional echoaortocardiography, standard echocardiography, and M-mode scanning. In both electrocardiographically gated and nonelectrocardiographically gated two-dimensional echoaortocardiograms of each patient, aortic-root dissections were clearly visualized. Because of the possibility of a false-positive diagnosis of an aortic-root dissection by previously reported criteria (including cases in the authors' experience and in the literature), the authors are convinced that the combination of two-dimensional and standard echoaortocardiography provides the most reliable echo diagnosis of this disease.