Regular exercise may diminish the risk for atherosclerotic vascular disease in patients with non-insulin-dependent (type II) diabetes and in the general population. The basis for this effect of exercise may be its ability to diminish or prevent hyperinsulinemia, insulin resistance, and/or increases in intra-abdominal adipose mass. These abnormalities are associated with premature atherosclerotic vascular disease, essential hypertension, type II diabetes, and certain dyslipoproteinemias, and most likely precede them. They also have been implicated in the pathogenesis of these disorders. We propose that the high prevalence of hyperinsulinemia and insulin resistance in individuals leading a western life-style accounts for the reported benefit of physical activity in preventing coronary heart disease in the general population. We also propose that exercise (and diet) are most likely to be effective when initiated in young individuals, before the onset of irreversible vascular alterations, and when life-style changes may be more acceptable. Early identification of such individuals may be possible on the basis of family history, the presence of components of the hyperinsulinemia-insulin resistance syndrome, and/or central obesity. One such group that may already have been identified is women with gestational diabetes.