Congenital nephrotic syndrome (CNS) is a rare disorder that presents within 3 months of birth. It is characterized by massive proteinuria, edema,hypoalbuminemia, hyperlipidemia,hypogammaglobulinemia, and hypercoaguability. Without meticulous medical care and eventual renal transplantation, affected infants generally die by 6 months of age.CNS can have primary and secondary etiologies. The most common is CNS of the Finnish type. As a primary etiology, its cause remains unknown. Less common primary etiologies include diffuse mesangial sclerosis, minimal change nephrotic syndrome, and focal segmental glomerulosclerosis. Secondary CNS consists of known etiologies for which specific therapy is aimed at the underlying disease. These include infections, such as syphilis,toxoplasmosis, cytomegalovirus, hepatitis, and human immunodeficiency virus. Other secondary causes are mercury intoxication, genetic malformation syndromes such as XY gonadal dysgenesis, and systemic illnesses such as systemic lupus erythematosus and amyloidosis.Congenital nephrotic syndrome in Finland (CNF) constitutes the majority of CNS cases in the world. Infants who have idiopathic CNS in other parts of the world follow a similar course as infants who have CNF. Those who have CNF are born preterm, are small for gestational age, and have large placentas that comprise more than 25% of the birthweight. Affected infants develop proteinuria prenatally, and most exhibit edema within the first week of life. Distinctive physical features include wide cranial sutures, large open fontanelles, small nose, wide-set eyes,low-set ears, and umbilical hernia. In general, they feed and grow poorly because of substantial loss of proteins, effects of edema, and increased incidence of pyloric stenosis and reflux. They require early diagnosis and aggressive medical and surgical intervention.Diagnosis can be initiated prenatally. Elevated maternal serum and amniotic fluid alpha-fetoprotein (AFP)levels during the 15th to 20th weeks of gestation may identify those at risk,particularly in families that have a prior history. Because an elevated AFP level is nonspecific and can indicate many other obstetric complications,ultrasonography is helpful. Genetic analysis provides a definitive diagnosis. CNF has been linked to a defect in chromosome 19q13.1 and more specifically, to the“nephrin” gene. The product of this gene is a protein associated with the function of the glomerular filtration barrier. Mutations cause CNF and may be implicated in other diseases that involve proteinuria. Genetic analysis also differentiates patients who are carriers from those who ultimately develop CNF.Treatment for infants who have CNF focuses on reaching an ideal weight and nutritional status for renal transplantation, the only cure for the condition. Medical management includes providing a high-calorie and high-protein diet, vitamin supplementation,albumin administration, and diuretic therapy. Attention is directed at preventing and treating infections and thromboembolic events for which these infants are at high risk. Patients eventually need bilateral nephrectomy combined with peritoneal dialysis for ultimate renal transplantation. CNF does not recur following renal transplantation, and catch-up growth and normalization of development can be achieved.Infants in whom CNS is not treated have a complex and bleak clinical course. In vitro genetic analysis offers new hope for recognition and early intervention. Further, improvements in medical care and solid organ transplantation extend the hope for cure and normalization of growth and development. For some patients, CNS is no longer a fatal disease.Inheritance of this rare disorder usually is autosomal recessive,but sporadic cases have been found. Localization of the nephrin gene and association of CNF with mutations have allowed for improved prenatal diagnosis and medical intervention.