Iguratimod, a methanesulfonanilide, is an anti-inflammatory drug for the treatment of rheumatoid arthritis that has been developed exclusively in Japan and China. It inhibits the production of immunoglobulins and various inflammatory cytokines (interleukin-1, -6 and -8 and TNF), and exerts anabolic effects on bone metabolism by stimulating osteoblastic differentiation and inhibiting osteoclastogenesis. On the molecular level, it inhibits the nuclear transcription factor NF-κB but not its inhibitor, IκBα. In addition to these immunomodulatory and other long-lasting effects, iguratimod inhibits cyclooxygenase-2, which provides a synergistic short-term action against pain and inflammation. Efficacy and tolerability are comparable to salazosulfapyridine, and probably also to methotrexate. Combination with methotrexate is synergistic in patients with insufficient response to methotrexate and does not significantly increase adverse events.