Idiopathic membranous nephropathy is the most frequent cause of nephrotic syndrome in adults. The natural course of idiopathic membranous nephropathy is characterized by a high incidence of spontaneous remissions. Some 50% of the patients reach end-stage renal disease. Treatment with corticosteroids alone is not efficacious; treatment with a combination of immunosuppressive drugs improves renal survival. However, because of the high incidence of spontaneous remissions and the risk of treatment-related toxicity, immunosuppressive treatment should be reserved for patients with proven renal insufficiency. Cyclophosphamide appears to be more efficacious and better tolerated than chlorambucil. Identification of high-risk patients at an early stage of the renal disease may contribute to a more efficient use of immunosuppressive treatment.