This report describes a subgroup of 52 elderly patients with obstructive hypertrophic cardiomyopathy in whom certain clinical and morphologic features differed importantly from many other patients with this disease. Ages ranged from 60-84 years (mean 69) and the vast majority (45 or 87%) were women. Echocardiographic examination showed relatively small hearts having only modest ventricular septal hypertrophy, associated with marked distortion of left ventricular outflow tract morphology. Sizeable deposits of calcium in the mitral anulus appeared to contribute to the outflow tract narrowing. In most elderly study patients. anterior excursion of the mitral valve leaflets was relatively restricted, and the systolic apposition between mitral valve and septum resulted from a combination of anterior motion of the mitral valve and posterior excursion of the septum. The vast majority of the patients (50 of 52) remained symptomatic (or only mildly symptomatic) for most of their lives and often did not develope severe and intractable symptoms until the sixth or seventh decade (ages 56-81 years; mean 66). Only 12 were improved by pharmacologic therapy; however, 14 of the 18 patients who underwent ventricular septal myotomy-myectomy or mitral valve replacement obtained symptomatic benefit from operation. In conclusion, obstructive hypertrophic cardiomyopathy in many elderly (and predominantly female) patients may assume a distinctive morphologic appearance and a progressive clinical course.