OBJECTIVES: To derive a claims-based severity index for rheumatoid arthritis (SIFRA) and examine its impact on prevalent rheumatoid arthritis (RA) patients in Turkey.  METHODS: Using the Turkish national health insurance database MEDULA (01JUN2009-31DEC2011), prevalent RA patients were identified.  Patients were required to be age 18-99, have two RA diagnoses ≥60 days apart and be continuously enrolled 1 year pre- (baseline period) and post-index date (follow-up), which was the first RA claim during the identification period (01JUN2010-31DEC2010).  The SIFRA score was derived for each patient. RA-related indicators were sub-grouped as clinical and functional status, extra-articular manifestations, surgical history and medications. The strength of each relationship was measured from 0=no relationship to 6=perfect relationship, and assessed by six board-certified, clinically active rheumatologists according to the Delphi panel method. The index was previously validated and applied to the U.S. Department of Veteran Affairs, Veterans Health Administration (VHA) data.  RESULTS: For the total of 1,920 identified RA patients, SIFRA scores ranged between 0 and 69.40, with a mean value of 14.21, and a standard deviation (SD) of 10.26. Mean SIFRA scores were 7.05 (49.57%), which consisted of clinical and functional status variables, followed by 6.32 (44.47%) for medications, 0.48 (3.40%) for radiology and laboratory findings, 0.32 (2.25%) for extra-articular manifestations (pulmonary nodules, subcutaneous nodules, vasculitis ever, Felty’s syndrome ever), and 0.04 (0.31%) for surgical history (cervical spine fusion, hand/foot joint replacement, foot joint/ankle/wrist fusion, total hip/knee/elbow/shoulder replacement). CONCLUSIONS: SIFRA demonstrated evidence of being a significant determinant for health care costs and biologic therapy use. This study suggests that SIFRA could be an important methodological tool to control for severity in RA-related outcomes research. Any comparative effectiveness studies in RA treatment should include severity scores in the analysis.