Hypertension is often associated clinically with diabetes as part of the insulin-resistance syndrome or as a manifestation of renal disease. Elevated systemic blood pressure accelerates micro- and macrovascular complications in diabetes. Vasoactive hormone pathways including the renin-angiotensin-aldosterone system (RAAS) appear to play a pivotal role in the pathogenesis and progression of diabetic complications and possible diabetes itself. Recent studies have increased our understanding of the complexity of the RAAS with identification of new components of this cascade including angiotensin-converting enzyme 2 and a putative renin receptor. Agents that interrupt the RAAS confer end-organ protection in diabetes via hemodynamic and non-hemodynamic mechanisms. Trials are investigating the possible role of RAAS blockade in the prevention of type 2 diabetes.