OBJECTIVE: The safety and efficacy of intravenous (IV) abatacept in patients with active RA unresponsive to methotrexate have been demonstrated in short-term (ST) studies in global populations and a ST, Phase III study in a Korean patient population. Abatacept's long-term safety and efficacy profile has been established in open-label global studies with treatment up to 5 years. The objective of this study was to determine the long-term safety and efficacy of abatacept in patients with RA from the ST Korean study. METHODS: This was an open-label long-term extension (LTE) of a Phase III, multicenter, randomized, double-blind, placebo-controlled study in which Korean patients who had received IV abatacept or placebo in the ST trial (169 days) were given the option to receive open-label abatacept to Day 1485 with 84 days' follow-up (total 1,569 days, ~4 years). RESULTS: A total of 105 patients were enrolled in the LTE (86.7% female, median age 49.0 years). Abatacept was generally well tolerated. Adverse events were mostly mild or moderate and no new safety signals were identified. Improvement in disease activity (assessed by ACR response and DAS28 [CRP]), physical function (assessed by KHAQ-DI), and quality of life (assessed by SF-36 score) were maintained in patients initially treated with abatacept or observed in patients who had switched to abatacept after placebo in the ST study. CONCLUSION: Long-term treatment with IV abatacept over 1485 days was generally well tolerated in Korean patients with RA. Additionally, the efficacy profile from the ST study was maintained over the LTE.