Nephrotic syndrome is a clinical condition or group of disorders that involves defective kidney glomeruli with massive proteinuria, lipiduria with edema, hypoalbuminemia, and hyperlipidemia. It is classified as either primary nephrotic syndrome (PNS), formerly termed idiopathic nephrotic syndrome, or secondary nephrotic syndrome.

The incidence of nephrotic syndrome for patients younger than 16 years of age is 2:100,000 to 5:100,000. For the total population, the incidence is 15.5:100,000.

For nephrotic syndrome, a glomerular cause is generally accepted. The specific initiating event or root cause producing the massive proteinuria is still undetermined, although an immune pathology is strongly suspected. The permeability of the glomerular basement membrane is altered and the capillary transport of albumin, an anionically charged molecule, is increased by a deficiency of sialic acid from the basement membrane.