OBJECTIVE To assess the prognostic significance of left ventricular mass and geometry in initially healthy persons with essential hypertension. METHODS An observational study of a prospectively identified cohort. METHODS University medical center. METHODS Two hundred and eighty patients with essential hypertension and no pre-existing cardiac disease were evaluated using echocardiography between 1976 and 1981. Two hundred and fifty-three subjects or their family members (90%) were contacted for a follow-up interview an average of 10.2 years after the initial echocardiogram was obtained; the survival status of 27 patients lost to follow-up was ascertained using National Death Index data. RESULTS Left ventricular mass exceeded 125 g/m2 in 69 of 253 patients (27%). Cardiovascular events occurred in a higher proportion of patients with than without left ventricular hypertrophy (26% compared with 12%; P = 0.006). Patients with increased ventricular mass were also at higher risk for cardiovascular death (14% compared with 0.5%; P less than 0.001) and all-cause mortality (16% compared with 2%; P = 0.001). Electrocardiographic left ventricular hypertrophy did not predict risk. Patients with normal left ventricular geometry had the fewest adverse outcomes (no cardiac deaths; morbid events in 11%), and those with concentric hypertrophy had the most (death in 21%; morbid events in 31%). In a multivariate analysis, only age and left ventricular mass--but not gender, blood pressure, or serum cholesterol level--independently predicted all three outcome measures. CONCLUSIONS Echocardiographically determined left ventricular mass and geometry stratify risk in patients with essential hypertension independently of and more strongly than blood pressure or other potentially reversible risk factors and may help to stratify the need for intensive treatment.