It is now well established that non-insulin dependent diabetes mellitus is characterized by insulin resistance. Independent data have suggested that essential hypertension also is associated with abnormal glucose tolerance and an impairment of insulin action. These observations have led to the hypothesis that insulin resistance and/or hyperinsulinaemia may provide a common pathophysiological basis for the high concordance of these two diseases in many individuals. The relationship between insulin resistance, diabetes and hypertension assumes additional importance when one considers that many antihypertensive medications may impair insulin sensitivity or insulin secretion, thus leading to a further impairment of glucose tolerance or deterioration of glycaemic control. In the present review, the epidemiological and pathophysiological evidence supporting this hypothesis will be examined and the implications for treating hypertension in the patient with diabetes will be discussed.