Objective: Patients with rheumatoid arthritis (RA) perceive sleep quality as an important component of their quality of life. Sleep is multi-dimensional and the objective is to investigate what aspects of sleep improve when patients are treated with abatacept. Methods: We used data from two randomized, double-blind clinical trials of abatacept in patients with active RA in this study: AIM and ATTAIN, in methotrexate and anti-TNF failures respectively. Sleep quality was assessed using the validated Medical Outcomes Study sleep questionnaire (MOS-sleep). The treatment groups were compared on the seven derived MOS-sleep scales: awakened short of breath or with headache, snoring, sleep adequacy, sleep disturbance, somnolence, and sleep problems Index I and II. In addition, sleep duration (in hours) and optimal sleep (yes vs no) based on the MOS-sleep module were compared. Items are scored 0-100 with higher scores indicating more of the attribute under consideration. Since all the attributes for the scale scores are negative, a smaller number is better except for sleep adequacy which is a positive attribute. Optimal sleep is a binary variable with one indicating optimal sleep, so a higher proportion on this variable is better. Results: There was no pertinent difference at baseline in the various items on the MOS sleep questionnaire or on the derived MOS sleep scales. Significant improvement in the abatacept group compared to control on sleep adequacy, sleep disturbance, somnolence and both sleep problem indices I and II were found. For both studies, sleep quantity was not significantly difference between treatment groups, but optimal sleep significantly improved in the abatacept vs control group: ATTAIN (18% vs -12%, p<0.0001) and AIM (16% vs 5%, p=0.0214). Conclusion: Treatment with abatacept improves several different aspects of sleep in RA patients. In particular, sleep disturbance and sleep problems given by index II are reduced, and optimal sleep is improved.