Primary nephrotic syndrome encompasses the spectrum of minimal change disease, focal segmental glomerulosclerosis, and related disorders. It is a common cause of morbidity and, more rarely, of mortality in children. Recent progress has permitted us to better understand the mechanism of proteinuria and how it causes the other findings of nephrosis. Developments related to the pathogenesis of nephrosis and why some patients develop focal segmental glomerulosclerosis are less striking, but recent studies have indicated useful directions for subsequent work in these areas. Finally, application of newer concepts to treatment has provided both a better prognosis for these diseases and decreased morbidity from treatment.