Six patients with aortic root dissection proved by angiography, surgery or autopsy, and six patients with aortic root dilatation were studied by echocardiography. Echocardiography was diagnostic in five or six patients with dissection and suggestive in the sixth, disclosing anterior and posterior dissection in three, anterior dissection in one and posterior dissection in one. The recording of a double echo in the aorta was the diagnostic feature. Angiography was diagnostic in four of the six patients, yielded a false negative result in one and was not performed in one. Six patients with dilatation had an enlarged aortic root by echocardiography. Left ventricular size, stroke volume, ejection fraction, aortic regurgitant flow and velocity of circumferential fiber shortening were calculated in 11 patients. Echocardiography was extremely helpful in the diagnosis, management and follow-up in patients with aortic dissection or dilatation.