Many acquired and familial renal diseases in man lead to kidney dysfunction and nephrotic syndrome. These diseases share a common pathological fate in the form of glomerular dysfunction and proteinuria. Classification of the disease is difficult because the onset of pathological appearance in congenital nephrotic syndrome (CNS) varies considerably. Recently, classification has been aided by applying molecular genetics to identify genes involved in the pathogenesis of proteinuria. Light has also been shed on the biology and mechanisms of glomerular filtration and the molecular pathogenesis of CNS.