Idiopathic membranous nephropathy (IMN) may have a variable course, with some patients entering spontaneous remission and others slowly progressing to renal failure. The disease is treatable, but the available treatments are not devoid of potential morbidity. We review the studies dedicated to finding prognostic markers. Although a number of clinical and histologic markers are associated with an increased risk of progression to renal failure, in many cases it is still impossible to recognize at presentation what will be the long-term outcome for a patient with IMN. More reliable are time-dependent predictors, such as the amount of proteinuria over time and complete or partial remission. However, this means that a physician should wait for months or even years before taking therapeutic decisions, with the risk of starting after renal or extrarenal complications have already developed. How to proceed will have to be dictated by a careful evaluation of the patient: Taking into consideration not only the risk of renal progression but also the possible extrarenal complications, we suggest starting a "specific" treatment for patients presenting with full-blown nephrotic syndrome or with increasing levels of serum creatinine, while specific treatment is not necessary for asymptomatic patients with subnephrotic proteinuria.