The presence of protein in urine is a common laboratory finding in children. Although proteinuria is usually benign, it can be a marker of a serious underlying renal disease or systemic disorder. 1 – 3 When proteinuria coexists with hematuria, the likelihood of clinically significant renal disease is higher. 1 , 2 Further, proteinuria represents an independent risk factor for the progression of nonglomerular or glomerular chronic kidney disease in children. 4 – 9 The Chronic Kidney Disease in Children study demonstrated that persistent proteinuria with a high urine protein-to-creatinine (UPr/Cr) ratio (more than 2 in patients with nonglomerular disease and more than in patients with glomerular disease) predicts significant chronic kidney disease progression. 7 The challenge for the primary care physician is to separate benign forms of proteinuria from those with clinical significance.