OBJECTIVES: Sleep issues have been reported by patients with rheumatoid arthritis (RA) and recently recommended as a clinical trial endpoint.  The objective of this study was to conduct a quantitative validation of the sleep disturbance and sleep adequacy subscales of the 1-week recall Medical Outcomes Study Sleep Scale (MOS-SS) in patients with RA. METHODS: Participants with self-reported RA were recruited via newspaper or online advertisements in two regions of the US. Participants completed measures in-person, then completed a one-week retest via mail.  Internal consistency of the MOS-SS subscales was evaluated using Cronbach’s α; test-retest reliability was assessed using Intraclass Correlation Coefficient (ICC). Pearson’s correlation coefficient was calculated to assess convergent validity of MOS-SS 1-week subscales with a Sleep Numeric Rating Scale (NRS). Known-groups validity was assessed using ANOVA to compare MOS-SS mean subscale scores with self-reported RA severity (mild, moderate, severe) and general health (very good, good, fair, poor). RESULTS: Participants (N=50) were 76% female, 72% White, mean age (SD) 49.4 (13.2) years and mean disease duration (SD) 13.7 (12.0) years. Cronbach’s α for sleep disturbance and adequacy subscales were 0.73 and 0.71, respectively. Mean sleep disturbance and adequacy subscale scores were 47.1 and 34.0 at baseline, 47.3 and 32.0 at 1-week follow-up (ICC=0.78 and 0.75), respectively. Correlations of the sleep disturbance and adequacy subscales with the Sleep NRS were r=0.43 (p=0.002) and r=0.45 (p=0.001), respectively. Mean sleep disturbance and adequacy subscale scores across RA severity and health status groups trended as hypothesized but were not significantly different. CONCLUSIONS: The MOS-SS sleep disturbance and sleep adequacy subscales demonstrated good internal consistency and test-retest reliability, modest convergent validity, and trended but did not significantly discriminate based on RA severity or general health. Further psychometric analysis in a larger sample of RA patients is needed to determine if these subscales could be useful in clinical trials.