The prevalence of electrocardiographic left ventricular hypertrophy was studied in a population of 19,622 men born and living in France, aged from 40 to 69 years, who volunteered to have a medical check-up at the health centre of preclinical investigations, Paris, between 1972 and 1977. Enquiries were made among local authorities and physicians to determine the number of deaths and their causes. During the follow-up (median 9.5 years), 1,285 deaths were recorded. The overall cardiovascular mortality was 384 deaths: 178 patients died of ischaemic heart disease, 66 of sudden death, 93 of cerebral vascular accident and 47 of various cardiovascular diseases. The presence of an electrocardiographic left ventricular hypertrophy increased the incidence of overall mortality and all causes of cardiovascular mortality in all age-groups. An analysis of survival after adjustment for age, systolic blood pressure, cholesterol level and smoking habits indicated that left ventricular hypertrophy is indeed a predictor of total cardiovascular mortality and of mortality due to ischaemic heart disease.