Membranous nephropathy is the most common cause of idiopathic nephrotic syndrome in adults. The frequency of secondary forms varies from 20 to 30 per cent. The principal causes appear to be systemic lupus erythematosous, drug therapy, malignancy and viral infection. The pathology includes normocellular glomeruli with subepithelial deposits on the outer surface of the glomerular basement membrane. Immunofluorescence studies reveal consistently IgG granular deposits. Prolonged high-grade proteinuria is common. Renal vein thrombosis is frequently associated. Persistent hyperlipidemia increases the risk of cardiovascular diseases. The course of idiopathic membranous nephropathy remains variable. Numerous factors affecting the prognosis of the nephropathy have been identified and should be considered for the decision of specific treatment and use of immunosuppressive therapy.