Treatment of hypertension with the major available antihypertensive classes results in a significant improvement in cardiovascular morbidity and mortality. However, there is controversy about whether specific classes of drug therapy have deleterious or beneficial effects on glucose and lipid metabolism. Myths and misconceptions have thus arisen. Although "old" classes of antihypertensives, such as diuretics and beta-blockers, seem to have deleterious effects on glucose and lipid metabolism, the "newer" agents appear to have either neutral or beneficial profiles. The long-term significance of these metabolic changes is still debated. It is known that insulin resistance plays a major role in the pathogenesis of hypertension and type 2 diabetes mellitus. There is increasing evidence that blocking the renin-angiotensin-aldosterone system by using angiotensin-converting enzyme inhibitors or angiotensin-receptor blockers favorably affects insulin sensitivity and, accordingly, decreases the incidence of new-onset type 2 diabetes mellitus.