Coexistent idiopathic hypertrophic subaortic stenosis (IHSS) and coronary arterial disease (CAD) was found in 10 patients studied because of disabling angina. Only one had experienced consistent relief of angina with nitroglycerin. All had systolic murmurs which had been ascribed to valvular stenosis or papillary muscle dysfunction. Mean patient age was 57 years. Nine were males. All patients were shown to have the characteristic hemodynamic and angiographic findings of classical IHSS. Coronary cineangiography revealed severe CAD in each patient. Precatheterization diagnosis of combined IHSS and CAD was difficult to make unless a very well-documented history of prior myocardial infarction was available, and clinical evaluation revealed the typical auscultatory and pulse contour changes of IHSS. In six of the patients clinical evidence alone was not sufficient to diagnose combined disease with any certainty. There is a significant incidence of IHSS in the coronary disease-prone age group. The possible coexistence of the two diseases has not been appreciated previously. Patients with IHSS and angina should be evaluated for CAD as they may benefit if therapy is directed at both disorders. Patients with CAD, angina, and systolic murmurs should be evaluated for possible IHSS, especially if coronary artery surgery is contemplated, since such therapy may be inappropriate or incomplete.