Membranous nephropathy is defined by the presence of immune deposits localized on the epithelial side of the glomerular basal membrane. Its mechanism has been elucidated through numerous experimental models and is thought to be the consequence of in situ formation of immune complexes. Membranous nephropathy is clinically discovered by a nephrotic syndrome of unknown long-term evolution: 25% of the patients undergo complete spontaneous remission and 20% show progressive renal failure. As of today, no prognostic criteria are available. Numerous studies using steroids, immunosuppressive agents, or a combination of both, have tried to modify the natural history of the disease, but none of these protocols clearly seem to have changed the course of the disease.