Membranous nephropathy is the most frequent cause of glomerulonephritis in adults with nephrotic syndrome. Approximately one quarter of the patients develop end-stage renal disease. Another quarter enters complete remission during follow-up. Treating all patients with membranous nephropathy with immunosuppressive drugs would unnecessarily expose at least one quarter of the patients to these toxic drugs. Identifying patients at highest risk would allow tailor-made treatment. Many risk factors have been found, such as male sex, HLA type DR3+/B8+, white race, advanced age, and tubulointerstitial changes or focal sclerosis found with renal biopsy. In addition, nephrotic syndrome, elevation of immunoglobulin G excretion or beta2-microglobulin excretion, low serum albumin, high serum cholesterol, an elevation of urinary excretion of complement activation products, impaired renal function at diagnosis, and, finally, hypertension are associated with a higher risk of renal function deterioration during follow-up. We have critically reviewed the literature and summarized the clinical significance of the above-mentioned risk factors in predicting subsequent renal function deterioration in patients with membranous nephropathy.