Idiopathic membranous nephropathy (IMN) is an autoimmune disease without specific aetiology and defined by proteinuria that is often in the nephrotic range and granular deposits of IgG among the glomeruli. It is the causative renal disease in about 3% of patients requiring dialysis. About 30% of patients have an unfavourable outcome and develop terminal renal failure, generally after 10 years. Massive proteinuria is the only reliable clinical predictor of the risk of renal failure.