OBJECTIVE: To clarify the efficacy and safety of abatacept for glandular and extraglandular involvements in Sjögren's syndrome (SS) associated with rheumatoid arthritis (RA). PATIENTS AND METHODS: We performed an open-label, prospective, 1-year, observational multicenter study (ROSE and ROSE II trials) for SS with RA. The primary endpoint was the remission rate as measured by SDAI at 52 weeks after initiation of intravenous abatacept. The secondary endpoints included the changes in the Saxon's test, Schirmer's test, ESSDAI and ESSPRI. Adverse events and adherence rates during the study period were also analyzed. RESULTS: 68 patients (36 in ROSE and 32 in ROSE II, all women) were enrolled in this study. The mean SDAI decreased significantly from 23.6±13.2 (±SD) at baseline to 9.9±9.5 at 52 weeks (P<0.05). Patients with SDAI remission increased from 0 (0 weeks) to 19 patients (27.9%) at 52 weeks. Saliva volume increased significantly from 2015.1±1695.4 (0 weeks) to 2311.3±1804.4 (24 weeks) mg/2 min (n=66, P<0.05). Tear volume increased significantly from 5.0±6.0 (0 weeks) to 5.6±6.3 (52 weeks) mm/5 min (n=52, P<0.05). Both ESSDAI and ESSPRI scores were significantly decreased at 12 weeks, and these responses were maintained up to 52 weeks. The rate of adherence to abatacept over the 52-week period was 83.8%. Twenty-two adverse events occurred in 15 patients, and 9 of these events were infections. CONCLUSION: Abatacept ameliorated both glandular and extraglandular involvements, as well as the systemic disease activities and patient-reported outcomes based on composite measures, in patients with SS associated with RA.