Background: Bucillamine (BCL), a treatment for rheumatoid arthritis, occasionally causes proteinuria. Renal specimens are reported to show segmental granular deposition of immunoglobulin G, associated with membranous nephropathy. Long-term course and optimal treatment have remained unknown, and were investigated here. Methods: We examined clinical records of 400 patients treated with BCL for rheumatoid arthritis, at our hospital from 1998 to 2003, finding 17 with proteinuria and biopsy-proven BCL-induced nephropathy. Results: In all 17 patients, proteinuria resolved without loss of renal function between 3 and 85 months after discontinuing BCL (14.1 ± 3.4). The only factor influencing time to remission was pathologic stage of membranous nephropathy (stage I vs. stage II or III: 11.5 ± 4.8 vs. 21.6 ± 3.3 months; p = 0.02). Maximal proteinuria, total amount of BCL, BCL exposure time, and use of prednisolone or other immunosuppressant agents did not significantly influence time until remission. Conclusion: The most important therapeutic step in treating BCL-induced nephropathy is to discontinueBCL. Prednisolone or other immunosuppressant agents might not be effective.