Data on the prognostic implications of left ventricular hypertrophy (LVH) in the Framingham Study based on routine ECG, echocardiogram (ECHO) and X-ray determination with 36 years of follow-up indicate that LVH has emerged as a powerful indicator of rapidly evolving lethal atherosclerotic disease, whether determined by ECG, ECHO or X-ray. Cardiovascular morbidity and mortality increase progressively with left ventricular muscle mass from lowest to highest values. The ECG and X-ray versions of LVH each independently contribute to the risk of cardiovascular events; each adds to the risk associated with the other, and those with both are at greater risk than those with either alone. Risk ratios associated with ECG-LVH are substantial and are greatest for cardiac failure and stroke, but coronary disease is the commonest and most lethal sequela. LVH is reversible, the anatomical variety more so than ECG-LVH, and reversal of this toward normal appears to confer greater benefit for the anatomical rather than the ECG manifestation of LVH. The risk of cardiovascular disease associated with LVH is not uniform, varying widely depending not only on whether there is concomitant ECG and anatomical evidence of hypertrophy but also on the associated hypertension, glucose intolerance, lipid profile and cigarette smoking habit. This suggests that there is much to be gained in correcting those associated risk factors which also promote the development of LVH.