The prevalence of and risk factors associated with echocardiographically determined left ventricular hypertrophy were examined in 4976 participants in the Framingham Heart Study (age, 17 to 90 years). Left ventricular hypertrophy was detected in 356 men (16%) and 513 women (19%). Prevalence increases dramatically with age (P less than 0.001), with 33% of men and 49% of women age 70 or older affected. A significant association between blood pressure and left ventricular hypertrophy is present and occurs at levels of systolic pressure below 140 mm Hg (age adjusted, P less than 0.001). There is a ninefold (women) to tenfold (men) increase from leanest to most obese group (age adjusted, P less than 0.001). In multivariate analysis, age, blood pressure, obesity, valve disease, and myocardial infarction are independently associated in both sexes. We conclude that left ventricular hypertrophy is a common echocardiographic finding for which several risk factors can be identified. These findings support weight reduction and blood pressure control for prevention or regression of this condition.