OBJECTIVES: To examine adoption, choice, and utilization of rheumatoid arthritis (RA) biologic therapies and the patient and plan characteristics associated with these in Medicare. METHODS: Nationally representative 2006–2008 5% Medicare Parts A, B, and D files were examined.  The sample (N=47,511) consisted of pooled annual cross-sections of fee-for-service beneficiaries with Part D coverage and >1 inpatient or 2 outpatient claims with RA diagnosis (ICD-9-CM 714.xx).  Logistic regressions with robust clustered standard errors were estimated to identify patient and plan characteristics associated with any biologics use, biologics use under Part B (i.e. physician administered infusion) versus Part D (i.e. self-injectable), and use of specific biologics under Part D. RESULTS: From 2006 to 2008, RA biologics use decreased slightly (15.0% to 14.0%).  The proportion of biologic users utilizing Part D biologics decreased from 60% to 50%.  Disabled or female RA patients were more likely (OR=1.3, 95% CI 1.2-1.5, for both) to use biologics; older patients were less likely (OR=0.5, 95%CI .4-0.5). RA patients in the South were more likely to use biologics relative to the Northeast (OR=1.3, 95% CI 1.2-1.5).  Among RA biologic users, patients in the Midwest (OR=0.5, 95% CI 0.4-0.7) or South (OR=0.6, 95% CI 0.5-0.8) were less likely to use Part D biologics relative to the Northeast.  Patients qualifying for Part D low-income subsidies (LIS) with minimal Part D cost-sharing were more likely to use Part D biologics compared to non-LIS patients (OR=2.6, 95% CI 1.8-3.8). Furthermore, non-LIS RA patients were more likely to use adalimumab (OR=1.5, 95% CI 1.1-2.1) if they were enrolled in plans that had more utilization management tools for etanercept; however, a similar effect was not noted in LIS patients. CONCLUSIONS: Strong geographic variation exists in utilization of RA biologics in Medicare.  Part D cost-sharing and utilization management tools also influence choice of biologics.