Proteinuria is a common laboratory finding in children. It can be identified as either a transient or a persistent finding and can represent a benign condition or a serious disease. A rapid but qualitative assessment of proteinuria can be made using dipstick or sulfosalicylic acid methods. More precise quantitation is obtained by measuring protein excretion in 24-hour urine samples or by calculating the protein/creatinine ratio in random urine samples. Orthostatic proteinuria is a benign condition characterized by the presence of protein in urine samples collected in the upright position during the day and its absence in samples collected in the supine position. Persistent proteinuria and proteinuria associated with hematuria or other signs of renal disease carry a more severe prognosis. The latter conditions require referral to a pediatric nephrologist for further evaluation, which may include renal biopsy.