Abstract Background: Assessing barriers to human papillomavirus (HPV) vaccination among a sample of physicians seeing Medicaid patients is an important step in understanding the diffusion of HPV vaccination to medically underserved populations. Purpose: The primary aim of this study was to assess physician barriers to immunizing Florida Medicaid patients against HPV. Methods: A sample of 800 providers was randomly selected from the Florida Medicaid Master Provider File. The sampling frame was restricted to providers who had a physical address in Florida, had billed claims or had an assigned panel that included 25 or more 9- to 17-year-old girls in the past year, and had a specialty of Pediatrics (Peds), Obstetrics and Gynecology (OBGYN), or Family Medicine (FM) that included internal medicine, general practice, and preventive medicine. In October 2009, physicians were mailed a survey that evaluated key areas related to HPV vaccination, including: 1) demographic and practice characteristics, 2) HPV information and knowledge, 3) barriers to HPV vaccination, 4) vaccine practices, and 5) vaccine recommendation practices. Physician barriers to immunizing patients were assessed using a 13 item scale. Physicians were asked to rate their level of agreement with a series of barriers to HPV immunization for their Medicaid patients (1 = strongly disagree, 5 = strongly agree). Items were summed and averaged to create a mean barrier score (range: 1 −5). Differences in mean barrier scores by physician specialty were assessed using a one-way ANOVA. Additionally, frequencies were obtained for each item on the barrier scale. Results: After removing physicians who were ineligible (n = 43), undeliverable surveys (n = 65), and duplicate surveys (n = 4), the response rate was 67.44% (n = 464). Among physicians who answered all barrier items (n = 458), the overall mean barrier score was 2.70 (SD = 0.72). Stratified by specialty, the mean barrier score was 2.65 (SD = 0.72) for Peds, 3.01 (SD = 0.66) for FM physicians, and 2.60 (SD = 0.64) for OBGYNs. FM physicians had a significantly higher mean barrier score than both Peds and OBYGNs, F(2,436) = 7.30, p = 0.0008. The three most common barriers to HPV vaccination where physicians reported they “strongly agree” were lack of adequate reimbursement (21.56%, n = 94), concerns about vaccine safety (19.18%, n = 84), and lack of timely reimbursement (17.66%, n = 77). Conclusions: Results indicate relatively low overall barriers to immunizing Medicaid patients against HPV. Physician reimbursement issues appear to be top barriers to immunizing Medicaid patients. Additionally, specialty appears to impact perceived barriers to HPV vaccination, with FM physicians indicating greater barriers than Peds or OBGYNs. These findings suggest that improvement in reimbursement procedures may increase HPV vaccination among medically underserved groups. Citation Information: Cancer Epidemiol Biomarkers Prev 2010;19(10 Suppl):B115.