Proteinuria (protein excretion > 300 mg/d) is an independent risk factor for the development of cardiovascular disease and renal failure. The finding of persistent proteinuria in otherwise asymptomatic patients often precedes the development of arterial hypertension and renal failure. When proteinuria is accompanied by arterial hypertension, blood pressure control can decrease the quantity of protein excretion but not the incidence of proteinuria. In this sense, converting enzyme inhibitors seem to possess a higher capacity to reduce proteinuria. Nevertheless, the effects of reducing proteinuria on renal function and cardiovascular risk remain to be elucidated. Microalbuminuria (urine albumin excretion oscillating between 30 and 300 mg/d) seems to be a predictor of cardiovascular disease in diabetic and nondiabetic subjects and has been established as a predictor for the development of diabetic nephropathy. Blood pressure levels and urinary albumin excretion correlate positively, and antihypertensive therapy of any kind decreases the quantity of albumin present in the urine. The role of increased albumin excretion in essential hypertension and in renal failure remains to be elucidated.