The nephrotic syndrome, an entity of multiple causes, is characterized by edema, proteinuria, hypercholesterolemia, and hypoalbuminemia. It occurs in the child or adult with primary renal disease or a systemic disease involving the kidney. The percutaneous renal biopsy has enabled clinicians to study the natural history of the underlying renal disease and to prognosticate more carefully the outcome of therapies. Other clinical features—age of onset, urinary protein selectivity, urinary enzyme concentrations—have been helpful as prognostic indexes. Immunofluorescent studies of renal tissue are valuable in diagnosis, prognosis, and patient management. Immunologic and inflammatory mechanisms are involved with the glomerular basement membrane, and further study of them may provide more specific and effective therapies. Corticosteroids are effective in the management of the nephrotic syndrome in children and, to a lesser degree, in adults. Azathioprine, cyclophosphamide, and methotrexate appear to be valuable in steroid-resistant and relapsing cases, although long-term experience with toxicity and survival time is limited at present.