The clinical usefulness of the Sokolow-Lyon voltage criteria in the assessment of electrocardiographic left ventricular hypertrophy (ECG LVH) is addressed. We prospectively studied 3,338 women and 3,330 men referred with hypertension, with an average follow-up of 11.2 years. The voltage amplitude sum SV1+max (RV5 or RV6) was calculated and ECG LVH was defined as a sum >or=3.5 mV. We adjusted survival for age, treatment status before presentation and a previous myocardial infarction or cerebrovascular accident. The risk of stroke, coronary heart disease (CHD) and cardiovascular disease (CVD) mortality increased significantly for each quantitative 0.1 mV increase in baseline electrocardiogram (ECG) voltage, in women within the range of 1.6-3.9% and in men 1.4-3.0%. After further adjustments for race, body mass index, smoking and systolic blood pressure, increasing voltage independently predicted CVD mortality in both men and women. In women, both increasing voltage and the presence of left ventricular hypertrophy (LVH) were predictors of stroke mortality, whereas in men this risk was attenuated. In men, the adjusted association between increasing voltage and CHD mortality tended to be stronger than in women. The use of different thresholds for the two genders made little difference. For stroke and CHD mortality, the population attributable fractions associated with LVH were 15.2 and 5.4% in women and 12.8 and 8.5% in men, respectively. In conclusion, the greater the baseline ECG voltage sum, the greater the associated CVD mortality risk. Women tended to have a high risk of stroke mortality owing to LVH despite adjustments.