In a 24-month period, 27 patients with idiopathic hypertrophic subaortic stenosis (IHSS), ages 65-80 years, were observed. Diagnoses were made by echocardiography (24 patients), cardiac catheterization (one patient), and both methods (two patients). The most common symptoms were angina (17 patients), dyspnea (13 patients), and syncope (11 patients). Two patients were asymptomatic, while another complained only of vague retrosternal chest discomfort with exertion. One asymptomatic patient had a completely normal physical examination, but electrocardiography (ECG) demonstrated a pattern of left ventricular hypertrophy. Another patient had an inconsistent apical holosystolic murmur. Two patients had alpha streptococcal endocarditis; neither was known to have pre-existing valvular disease. Fourteen patients had ECG criteria for left ventricular hypertrophy (LVH). Three patients were known to have associated aortic valve disease. The symptoms of IHSS may be nonspecific; asymptomatic patients with and without cardiac murmurs may be observed. Coexisting valvular disease, coronary artery disease, and bacterial endocarditis were documented. Patterns of myocardial infarction on ECG were not seen in these 27 patients.