Idiopathic membranous glomerulonephritis is the most common cause of adult nephrotic syndrome. It is relatively a rare disorder in children. The hallmark of membranous nephropathy is the presence of immune complexes in the subepithelial region of the glomerular capillary wall. The source of these immune complexes is not known. The nephritogenic antigen may be intrinsic to the glomerulus or exogenous. The antigen may be deposited in the subepithelial region, then bind antibodies and immune complexes are formed or antigen may be part of circulating immune complexes. The pathogenesis of human membranous nephropathy is unknown. The antigenic equivalent to megalin in experimental membranous nephropathy has not been identified in humans. An increased incidence of this disorder has been reported with HLA-DR3 in Greece and England. It has been reported in identical twins.