Clinical and autopsy evidence support the increased risk of atherosclerotic disease in diabetes mellitus (DM). However, mechanisms other than arterial occlusion may also contribute to clinical syndromes often assumed to be atherosclerotic in origin. There is considerable geographical variability in the frequency of arterial disease in the diabetic. Glucose intolerance short of unequivocal DM is found in some (though not all) populations to carry increased atherosclerotic risk. Morbidity and mortality data suggest that women are particularly vulnerable (as with DM). The Whitehall prospective study of cardiovascular mortality shows that risk does not rise smoothly with increasing degrees of glucose intolerance but that it doubles sharply at the 95th percentile of the 2-h post-glucose blood sugar distribution.