Proteinuria is a common finding in adults in primary care practice. An algorithmic approach can be used to differentiate benign causes of proteinuria from rarer, more serious disorders. Benign causes include fever, intense activity or exercise, dehydration, emotional stress and acute illness. More serious causes include glomerulonephritis and multiple myeloma. Alkaline, dilute or concentrated urine; gross hematuria; and the presence of mucus, semen or white blood cells can cause a dipstick urinalysis to be falsely positive for protein. Of the three pathophysiologic mechanisms (glomerular, tubular and overflow) that produce proteinuria, glomerular malfunction is the most common and usually corresponds to a urinary protein excretion of more than 2 g per 24 hours. When a quantitative measurement of urinary protein is needed, most physicians prefer a 24-hour urine specimen. However, the urine protein-to-creatinine ratio performed on a random specimen has many advantages over the 24-hour collection, primarily convenience and possibly accuracy. Most patients evaluated for proteinuria have a benign cause. Patients with proteinuria greater than 2 g per day or in whom the underlying etiology remains unclear after a thorough medical evaluation should be referred to a nephrologist.