BACKGROUND The actual prognosis of hypertrophic cardiomyopathy, a disorder previously thought of to be notorious for an increased risk of untimely death is poorly defined. OBJECTIVE The present study describes the findings of patients with Hypertrophic Cardiomyopathy followed for more than nineteen years in a large clinic population. METHODS A clinic population of 113 patients with Hypertrophic Cardiomyopathy was prospectively studied to assess cardiac mortality in the overall groups and in selected subgroups commonly thought to be at high risk for sudden death. Diagnosis of hypertrophic cardiomyopathy was based on the presence of left ventricular hypertrophy without a known cause. Left ventricular hypertrophy was determined by echocardiography. RESULTS During follow-up there were 11 cardiac and 2 non cardiac deaths. The annual cardiac mortality was 1% (95% confidence interval 0.2-1.8%). Relative risk for cardiac death was not significantly different in the presence of young age (< 30 years), family history for Hypertrophic Cardiomyopathy (HCM) and sudden death, history for syncope or previous cardiac arrest or both, ventricular tachyeardia on 24-hour, holter monitoring or operation for refractory symptoms and out-flowtract obstruction. CONCLUSIONS HCM has a relatively benign prognosis (1% cardiac annual mortality) that is 2-4 times less than previously thought. These findings might have important consequences for risk assessment in individual patients. Echocardiography is obligatory to determine the presence, and extent of myocardial hypertrophy. In addition, the technique allows differentiation between Hypertrophic Cardiomyopathy and Athlete's Heart.