The records of 208 patients with the nephrotic syndrome seen in the Children's and Infants' Hospitals of Boston from 1926 to 1948 have been reviewed. The main criteria found for differentiating between lipoid nephrosis and the nephrotic stage of chronic glomerulonephritis have been the presence of hypertension or azotemia for longer than one month in patients with the latter disease, which occurs more frequently in children over four years of age. Other features of the two diseases may be indistinguishable. Nonetheless, it is desirable to differentiate between them, as apparently few if any patients recover from the nephrotic syndrome if the evidences of glomerulonephritis are clear-cut. Lipoid nephrosis is characterized by the insidious onset of edema in young children, usually between the ages of one and four. Findings include edema, hypoproteinemia, hypercholesterolemia and heavy proteinuria. Blood pressure may be elevated for short periods, but rarely over one month. Microscopic hematuria does not exclude the diagnosis, though macroscopic hematuria is usually evidence of glomenular involvement. Symptoms and findings in lipoid nephrosis may persist for from one to three years without specific therapy. Exacerbations with infection, followed by remissions shortly after the infection, and remission soon after the onset of the disease are relatively common. Prognosis is not related to the number or duration of exacerbations. Death before 1942 was chiefly due to an intercurrent infection. Since 1942, with the advent of sulfadiazine and the newer antibiotics, death from infection has become less common, and has usually occurred at home, presumably because treatment was not promptly instituted. There is apparently no constitutional defect in these children before the onset of the disease, and growth and development are normal after recovery. No form of treatment has been found wholly satisfactory. Paracentesis, transfusion and low salt diet are the most common supportive measures used here. Antibiotics are valuable during infections and have apparently lowered the mortality of the disease in recent years. Focal sources of infection should be eliminated by operative procedure only when surgical intervention is definitely indicated. Injections of salt-poor concentrated human serum albumin and the induction of measles are being evaluated as methods of inducing a diuresis. In this series approximately one half of the patients with a clinical diagnosis of lipoid nephrosis have apparently recovered completely without residual disease, while a small number show persistent albuminuria or hypertension. It is hoped that with closer supervision of the patients and with adequate chemotherapy, this figure can be significantly increased in the future.