To assess whether echocardiographic and electrocardiographic detection of left ventricular hypertrophy could predict cardiovascular morbid events in patients with uncomplicated essential hypertension, we followed 140 men for a mean of 4.8 years. Initial echocardiographic measurements of left ventricular mass were normal (less than 125 g/m2 body surface area) in 111 patients and revealed hypertrophy in 29 patients. Morbid events occurred in more patients with hypertrophy on echocardiography (7 of 29, 4.6/100 patient-years) than with normal ventricular mass (7 of 111, 1.4/100 patient-years; p less than 0.01). Electrocardiography showed hypertrophy in too few patients to be of predictive value. Multiple logistic regression analysis showed that left ventricular mass index had the highest independent relative risk for future events and that systolic and diastolic pressures and age had slightly lower relative risks. In men with mild uncomplicated hypertension, left ventricular hypertrophy detected by echocardiography identifies patients at high risk for cardiovascular morbid events and is a significant risk factor for future morbid events independent of age, blood pressure, or resting ventricular function.