We tested the hypothesis that the voltages of QRS on ECG improve risk stratification in hypertensive patients without left ventricular hypertrophy on ECG. We studied 2042 initially untreated patients with hypertension (mean age 49 years, 46% women) without left ventricular hypertrophy on ECG and no history of cardiovascular disease. At entry, all patients underwent diagnostic tests, including 24-h ambulatory blood pressure monitoring and echocardiography. Among the different ECG voltages, the R wave in lead aVL showed the closest association with left ventricle (LV) mass (r = 0.31; P < 0.001), followed by the R wave in D1 (r = 0.25) and the S wave in V3 (r = 0.22). Patients were followed up for a mean of 7.7 years (range 1-22 years), and treatment was tailored individually. During follow-up, there were 188 major cardiovascular events. The relationship between LV voltage and outcome was assessed using a Cox model with adjustment for age, sex, diabetes, smoking, total cholesterol, serum creatinine, LV mass on echocardiography and average 24-h ambulatory blood pressure. A 0.1 mV higher R wave voltage in lead aVL was associated with a 9% higher risk of cardiovascular disease (95% confidence interval = 0.04-0.15%; P < 0.001). Other ECG voltages and minor repolarization changes were not related to clinical outcome. Our results show for the first time that the voltage of the R wave in lead aVL improves cardiovascular risk stratification in hypertensive patients without left ventricular hypertrophy on ECG. Its prognostic value is independent of LV mass on echocardiography and 24-h ambulatory blood pressure.