During a five year period, idiopathic hypertrophic subaortic stenosis was diagnosed in nine patients 70 to 79 years of age and in 26 patients 20 to 66 years of age who were referred to the cardiology division of the Long Island Jewish-Hillside Medical Center because of symptomatic heart disease. Only one of the older patients, compared with 19 of the younger ones, was referred with the correct diagnosis. Coronary artery disease with papillary muscle dysfunction was incorrectly diagnosed in four of the older patients. Cardiac catheterization confirmed the diagnosis of idiopathic hypertrophic subaortic stenosis in all of the 26 younger patients and in five of the nine older ones; diagnosis was based on typical echocardiographic features in the other four patients. Symptoms, physical findings, and electrocardiographic observations were similar in both groups. Aortic valve calcification was found in one younger patient and three older ones. The ratio of women to men was higher in the older group (7:2) than in the younger group (12:14). Coronary artery disease was more frequent in the older patients (three of five, compared with six of 26). Our experience indicates that idiopathic hypertrophic subaortic stenosis is not rare during the eighth decade. The diagnosis should be considered in any patient with an unexplained appropriate heart murmur, and definitive studies, such as echocardiography, should be done. As with any condition, proper management depends on accurate diagnosis.