We examined the 10-year outcome of 107 patients with hypertrophic cardiomyopathy and massive myocardial hypertrophy as assessed by echocardiography. These patients demonstrated excess mortality in comparison with their expected survival with respect to a general population of individuals (10-year survival 77% vs 95%, P < .001). Adverse events occurred primarily in the youngest and oldest patients. Sudden cardiac death was the most frequent cause of death among the young (overall survival 80%), whereas other causes predominated in older patients (overall survival 31%). For patients aged 30 to 59 years, survival was 97%, no different from their expected survival. Patients with hypertrophic cardiomyopathy and massive hypertrophy identified by echocardiography are at increased risk of death, but this risk is related to age at presentation. Sudden cardiac death is the primary cause in those who are young, whereas other causes predominate in older patients. Middle-aged patients with massive hypertrophy do not experience an excess mortality.