Diabetes mellitus is associated with severe and premature cardiovascular disease. The reasons for this have not been identified. It is now apparent that diabetics often have elevated circulating insulin levels compared to non-diabetics. In non-insulin dependent diabetes this is due to the associated obesity while in insulin treated diabetics exogenous insulin is responsible for hyperinsulinaemia between meals and at night. Two reports of high insulin levels in non-insulin dependent diabetics with cardiovascular disease are consistent with clinical and epidemiological studies linking hyperinsulinaemia with coronary, cerebral and peripheral arterial disease in non-diabetics. The arterial wall is an insulin sensitive tissue. Insulin promotes proliferation of arterial smooth muscle cells and enhances lipid synthesis and low density lipoprotein receptor activity. Insulin also promotes experimental atherosclerosis in a number of species. The evidence linking hyperinsulinaemia to the cardiovascular complications and diabetes is suggestive but incomplete and much more information on predictive factors for arterial disease in diabetes is urgently required. Diabetes mellitus is associated with severe and premature cardiovascular disease (reviewed by Stout 1982). Ischaemic heart disease, stroke and peripheral vascular disease are all more common in diabetics, particularly diabetic women. Although there is evidence for the existance of a specific diabetic cardiomyopathy, much of the cardiovascular disease in diabetics is due to atherosclerosis and its complications. Arterial disease in diabetics in distinct from microvascular disease affecting capillaries, and does not differ morphologically or biochemically from atherosclerosis in non-diabetics. The reason for the increased incidence of atherosclerosis in diabetes has not been established. Both non-insulin dependent and insulin dependent diabetes appear to be associated with cardiovascular disease.(ABSTRACT TRUNCATED AT 250 WORDS)