Diabetes mellitus rate is rising worldwide and is now recognized as the most common cause of endstage renal disease and blindness among adults, and a major risk factor for cardiovascular disease. Diabetics present more extensive atherosclerosis, and particularly, the type 2 diabetes mellitus patients are often obese, hypertensive, and dyslipidaemic subjects, sharing the criteria of the metabolic syndrome. Nowadays, the reninangiotensin system (RAS) can be considered a cascade of peptide hormones which play an important role in the development of several cellular and hemodynamic alterations among diabetics. Diabetes mellitus is now considered an inflammatory disease, since its origin in either type 1 or type 2, and there is growing evidence that insulin resistance, nephropathy, increased thrombotic risk, and endothelial dysfunction are all linked to RAS activation. In recent years, several studies showed the clear efficacy of angiotensin-converting enzyme inhibitors and angiotensin receptor blocking agents in reducing vascular complications and metabolic disorders. However, the precise role of the RAS blockade, including aldosterone inhibition, in modifying the morbidity and mortality associated with diabetes, is waiting for large, randomized and controlled clinical trials.