The echocardiographic findings of eight patients with hypertrophic cardiomyopathy without outflow obstruction (HMC) and of 15 normal (Norm) individuals are presented.The characteristic features in HMC were: (1) interventricular septal width much greater than normal (HMC = 2.5 ± 0.3 cm, Norm = 1.0 ± 0.2 cm,P< 0.005); (2) normal or only slightly increased posterior left ventricular wall thickness; (3) the ratio of interventricular septal to posterior wall thickness ≧2.0; (4) ejection fraction greater than normal (HMC = 0.76 ± 0.08, Norm = 0.68 ± 0.06,P< 0.025); (5) reduced velocity of the early diastolic closing motion of the anterior mitral leaflet (HMC = 60 ± 23 mm/sec, Norm = 124 ± 29 mm/sec,P< 0.005); (6) absence of abnormal systolic movement of the anterior mitral valve, as seen in hypertrophic obstructive cardiomyopathy. The diagnosis of hypertrophic cardiomyopathy can be made with echocardiography, even when outflow tract obstruction of the left ventricle is absent.