In patients with hypertrophic cardiomyopathy, wide-angle two-dimensional echocardiography is capable of detecting diverse patterns of myocardial hypertrophy that are often more extensive than may be appreciated by M-Mode echocardiography alone. In the vast majority of patients with hypertrophic cardiomyopathy the distribution of left ventricular hypertrophy is 'asymmetric'. Left ventricular wall thickening commonly involves substantial portions of the ventricular septum and free wall but rarely extends into the posterior segment of free wall (through which the M-mode beam passes). Four basic patterns of distribution of left ventricular hypertrophy may be identified by two-dimensional echocardiography in patients with hypertrophic cardiomyopathy. Most frequently (52% of patients) hypertrophy involves both the ventricular septum and anterolateral free wall (Type III). In other patients, hypertrophy is confined to the anterior portion of ventricular septum (Type I), involves the entire septum but not the free wall (Type II), or is limited to regions of the left ventricular wall other than the basal anterior ventricular septum (Type IV)--i.e. posterior segment of septum, anterolateral free wall, or septum in its apical one-half (apical hypertrophic cardiomyopathy). In patients with morphologic Type IV, the sites of left ventricular hypertrophy are inaccessible to the path of the conventional M-mode beam and the diagnosis of hypertrophic cardiomyopathy can only be established with two-dimensional echocardiography. Patients with the most marked and widespread hypertrophy involving the septum and free wall (Type III) more frequently demonstrated moderate to severe functional limitation, the pattern of left ventricular hypertrophy on electrocardiogram, and subaortic obstruction at rest produced by systolic anterior motion of the mitral valve in the presence of a small left ventricular outflow tract.