A common mechanism which may be involved in the development of hypertension in both type I and type II diabetes mellitus is a deficiency of insulin at the cellular level. Observations from a number of laboratories suggest that impaired cellular response to insulin rather than hyperinsulinemia predisposes to increased vascular smooth muscle tone (the hallmark of hypertension in the diabetic state). This review presents some of the data which suggest that there is a relationship between impaired cellular action of insulin, altered cellular calcium metabolism and the development of hypertension.