The striking clinical and pathologic features of hypertrophic cardiomyopathy have been defined almost exclusively in the young. Little is known about this condition in the elderly, although it is assumed to be part of a single disease. Accordingly, we studied 28 patients who were 65 years of age and older (mean age, 72 +/- 6.4 years) who were diagnosed as having hypertrophic cardiomyopathy by M-mode, two-dimensional, and Doppler echocardiography and compared them with a group of 28 consecutive patients with this disease who were younger than 40 years of age (mean age, 26 +/- 9.5 years). No clinically detectable differences existed between the two groups, except for an increased incidence of mild hypertension in the elderly. Echocardiography in both groups showed hypertrophy with a small left ventricular cavity, and Doppler outflow tract velocity or cardiac catheterization in most patients showed systolic anterior motion of the mitral valve or a systolic outflow tract gradient or both. Significant differences existed between both groups, however, concerning left ventricular size and shape. The elderly group had a predominantly ovoid cavity contour with normal septal curvature. In contrast, in the young group, a markedly abnormal cardiac shape predominated (p less than 0.0001) with a crescent-shaped left ventricular cavity and a reversed curvature of the interventricular septum. The right ventricular free wall was prominent by echocardiography in the young compared with the elderly group (p less than 0.001). Apart from a more frequent history of mild hypertension in the elderly, likely related to age, these findings show that hypertrophic cardiomyopathy, when present in the elderly, has similar clinical features to that in the young.(ABSTRACT TRUNCATED AT 250 WORDS)