BACKGROUND: The long-term efficacy of infliximab (IFX) for patients with refractory ulcerative colitis (UC) is unclear. The aim of this study was to assess the long-term outcomes of IFX treatment in patients with refractory UC. METHODS: Thirty-three patients with refractory UC who received IFX treatment at Kyoto University Hospital between 2003 and 2013 were retrospectively evaluated. IFX intensification was defined as a dose escalation (up to 10 mg/kg) and/or shorter intervals between infusions (every 4-6 weeks). RESULTS: Of the 33 patients who received scheduled infusions of IFX, 24 (72.7%) achieved clinical remission within 8 weeks after initiating IFX treatment. Of these 24 responders, 17 (70.8%) experienced a relapse of UC and required IFX intensification, and 16 (66.7%) eventually maintained clinical remission with IFX treatment, including IFX intensification. Of the 33 patients, 6 (18.2%) underwent colectomy during IFX treatment. Multivariate regression analysis showed that a serum C-reactive protein (CRP) concentration <5 mg/L two weeks after starting IFX was a predictor of a positive clinical response to IFX induction therapy. No severe adverse events occurred in UC patients treated with IFX. CONCLUSION: IFX intensification was necessary for long-term maintenance of remission and to prevent colectomy in patients with refractory UC.