OBJECTIVES: This secondary analysis of  REFLECTIONS, a prospective observational study of patients initiating on medications for fibromyalgia, compared patient, clinical, and treatment characteristics between United States (US) and Puerto Rico (PR). METHODS: Baseline data were collected from July 2008 through May 2010 via physician surveys, office visit forms, and telephone interviews in 58 care settings in the US and PR. RESULTS: Study patients included 1539 (90.5%) treated in the US and 161 (9.5%) in PR.  Patient characteristics differed for mean age in years (53.8 PR vs. 50.0 US, p<.001), body mass index (30.4 PR vs. 31.4 US, p=.049) and race/ethnicity (98.1% Hispanic PR vs. 91.4% Caucasian US). Patients in PR versus the US were more likely to have a lower category of economic status and less likely to be privately insured.  PR patients had more total concomitant diseases including back pain and depression (all p<.001).  Times to first symptom, diagnosis, and prescription were shorter in PR than US (all p<.01).  Patients in PR also reported more severe pain, pain interference, and greater disease impact via the Brief Pain Inventory and the Fibromyalgia Impact Questionnaire (all p<0.001). Treatment patterns also differed with US patients more likely to be prescribed opioids (5.6% PR vs. 26.2% US) and exercise (81.4% PR vs. 90.3% US), but less likely to be prescribed NSAIDS (55.9% PR vs. 23.6% US), (all p<.001). Despite the strong evidence for efficacy, cognitive behavioral therapy was prescribed infrequently (3.1% PR vs. 4.7% US, p=.36). CONCLUSIONS: :  To the best of our knowledge, this is the first study to describe patient and treatment characteristics for patients with fibromyalgia in PR.  Patient, clinical, and treatment characteristics of REFLECTIONS patients in PR differed in several respects from the US cohort. It is unknown whether these findings are generalizable to all fibromyalgia patients in the US and PR.