Hypertrophic cardiomyopathy is a primary myocardial disorder with an autosomal pattern of inheritance, characterized by asymmetric left ventricular hypertrophy with myocyte and myofibrillar disarray. Approximately 30% to 50% of all cases are accounted for by mutations in the beta-cardiac myosin heavy chain gene on chromosome 14q1. Recent linkage analysis led to the association of the disease with additional loci on chromosomes 1q3, 11p13-q13, and 15q2, but the underlying gene defects are as yet unidentified. To date, about 34 mutations of the beta-cardiac myosin heavy chain gene have been described and shown to have important prognostic implications. Definite genotype-phenotype correlations have been described; however, wide diversity in cardiac morphology, pathophysiologic features, and clinical manifestations is still evident, even within the same family. The disease has an annual mortality of approximately 3%, related to both progressive heart failure and sudden cardiac death. Not only diastolic but also progressive systolic dysfunction with cavity dilatation occurs in a minority of patients with severe left ventricular hypertrophy. These patients usually have a poor prognosis, especially when atrial fibrillation ensues. Sudden death often occurs in young, asymptomatic or mildly symptomatic patients. The degree of hypertrophy and the presence of a pressure gradient are of little prognostic significance. Nonsustained ventricular tachycardia is associated with a poor prognosis in the presence of a history of syncope.