Nephrotic syndrome is characterized by protein loss in the urine, hypoalbuminemia, hyperlipidemia and edema. Several diseases cause a nephrotic syndrome, as they damage the glomerular podocytes. These specialized epithelial cells, together with endothelial cells of the glomerular capillaries and the basal membrane, form a filter that retains plasma proteins in the circulation. A disturbance of this filter causes proteinuria. The three most common primary glomerular diseases are minimal change, membranous glomerulonephritis, and the primary focal segmental glomerulosclerosis. The familiar forms are rare; however, the identification of the relevant gene defects has greatly advanced our understanding of podocyte function as well as the pathogenesis of nephrotic syndrome.