Left ventricular hypertrophy (LVH) is a cardiac end-organ response to increased pressure or volume load. For the past 40 years the electrocardiogram (ECG) has been used in the Framingham Heart Study for the detection of LVH. There is an increased risk of developing coronary heart disease following the appearance of LVH on the ECG. ECG LVH also carries a high risk for mortality. The overall risk of mortality in subjects with ECG LVH exceeds that following myocardial infarction. Over the past three decades there has been a significant decline in prevalence of ECG LVH concomitant with increased utilization of antihypertensive drug therapy. The recent introduction of echocardiography into the Framingham Heart Study has resulted in the development of new echocardiographic criteria for LVH. Echocardiographic LVH is more prevalent than ECG LVH. Corresponding prevalence rates for these two methods (per 1,000) are 174 vs. 24, respectively. Ambulatory ECG monitoring documents an association of echocardiographic LVH with increased risk for ventricular arrhythmias. Data from Framingham and elsewhere suggest that echocardiographically defined LVH is an important predictor of risk for cardiovascular disease morbidity and mortality. The extent to which prevention or regression of LVH, in response to antihypertensive drug therapy will alter the substantial risks associated with this condition, awaits additional investigation.