We encountered a case of methicillin-resistant Staphylococcus aureus (MRSA)-induced septic arthritis after anterior cruciate ligament (ACL) reconstruction. A 20-year-old woman underwent left double-bundle ACL reconstruction by use of the hamstring tendon 18 months after her injury. She had a fever higher than 39 degrees C, and swelling of the left knee developed on day 5 after surgery. The white blood cell count was 19,500/mu L, and the C-reactive protein level was 16.9 mg/dL. Arthroscopic debridement with joint lavage was performed on day 7, followed by intermittent articular irrigation. Because the arthritis was not remitted, arthroscopic debridement with joint lavage was repeated, and the reconstructed ligarnent and hardware were removed on day 10. Intermittent articular irrigation was continued, but the arthritis still was not remitted, so a third arthroscopic debridement with joint lavage was performed on day 22. After treatment, continuous articular irrigation had been performed for 14 days until culture negativity of synovial fluid was confirmed. After methicillin-resistant Staphylococcus aureus was identified, vancomycin hydrochloride (2 g) was systemically administered for 29 days until the test for C-reactive protein became negative. Joint mobilization and revision ACL reconstruction by use of bone-tendon-bone were performed 2 months and I year, respectively, after the primary surgery.