To determine the common morphological characteristics of hypertrophic cardiomyopathy (HCM) by ventriculography from a right anterior oblique projection, diaphragmatic and free wall configurations were analyzed in 15 patients with obstructive HCM (HOCM), 32 patients with nonobstructive HCM (HNCM) and 17 controls. There was a convexity extending into the left ventricle in the right anterior oblique projection due to hypertrophy of the interventricular septum (IVS) in all patients with HCM. The peak convexity, where septal thickness was maximal (M point), was closer to the base in HOCM than in HNCM. Due to this convexity, the left ventricle showed a catenoid-shaped distortion at the M point. The distortion was severer in HOCM than in HNCM. Left ventricular free wall (LVFW) thickness was measured at the base and near the apex. LVFW thickness in HOCM decreased toward the apex, similar to that in controls, but in 17 of 32 HNCM (53%) LVFW thickness increased toward the apex. Cardiac index and stroke index in HCM were significantly smaller than those in controls. There was a significant correlation between the position of the M point and stroke index in HCM. These results indicate that a common morphological characteristic of HCM on the diaphragmatic side is the existence of a convexity extending into the left ventricle, and that cardiac performance in HCM is greatly influenced by the nature of the convexity. Myocardial abnormality seems to exist primarily at the base of the IVS in HOCM, and primarily in the lower part of the IVS and LVFW in HNCM.