Proteinuria is a sign of abnormal excretion of protein by the kidney but is a nonspecific term including any or all proteins excreted. In contrast, albuminuria specifically refers to an abnormal excretion rate of albumin. Microalbuminuria refers to an abnormally increased excretion rate of albumin in the urine in the range of 30-299 mg/g creatinine. It is a marker of endothelial dysfunction and increased risk for cardiovascular morbidity and mortality especially, but not exclusively, in high-risk populations such as diabetics and hypertensives. Testing for microalbuminuria is now made easy by in-office dipstick tests (semiquantitative) and widely available laboratory testing (quantitative). Physicians should screen all diabetics for albuminuria and strongly consider screening hypertensives to identify those at higher risk for cardiovascular disease. Appropriate intervention, including use of drugs that block the renin-angiotensin-aldosterone system, may be appropriate in such cases as suggested by the American Diabetes Association and the Seventh Report of Joint National Committee on the Prevention, Detection, Evaluation, and Treatment of High Blood Pressure.