Dilatation of the ascending aorta, a frequently reported sign of aortic stenosis, was assessed in 47 patients for whom aortic angiograms has been recorded. Twenty-eight of the patients had rheumatic valvar disease and 19 had congenital aortic stenosis. A simple ratio between the maximal width of the mid-ascending aorta and the width of the aortic root was calculated. Patients with congenital aortic stenosis had significantly greater supravalvar aortic dilatation than did those with rheumatic aortic valve involvement. There was no correlation between the pressure difference across the aortic valve and degree of dilatation of the ascending aorta.