13 Background: An outreach registry of Breast Health Center patients was developed in 2006 to evaluate the effectiveness of mobile mammography among the medically underserved. Registry included collection of medical record data, demographic data, and answers to a questionnaire about perceptions of breast cancer screening. Here, we examine barriers to mammography. Methods: Between April 2006 and May 2011, 9,082 women were registered. Data from registrants’ first screening visit (n= 8,916) were analyzed using multivariable logistic regression examining three outcomes identified as barriers to mammography: cost, fear of pain during the procedure, and fear of receiving bad news. Two-tailed p<0.05 was considered significant. Results: The majority of registrants were black (54%), uninsured (74%), screened on a van (83%), resided in the greater St. Louis region (84%), had an annual income <$20,000 (87%), and reported a good or excellent experience as part of the outreach program (92%). Fears of cost, mammogram-related pain, and bad news were reported by 40%, 13%, and 13% of registrants, respectively. Regression analyses revealed that being employed (odds ratio [OR] 1.109, p=0.0323) and living in the Bootheel of Missouri (OR 2.319, p<0.0001) were associated with a higher likelihood of perceiving cost as a barrier to mammography, while those who had insurance (OR 0.439) and were Hispanic (compared to non-Hispanic [NH] whites [OR 0.338]) were less likely to report cost as a barrier (both p<0.0001). Registrants who were screened on the van (OR 1.633), had insurance (OR 1.391), and were NH black (OR 1.324) were more likely to report fear of procedural pain as a barrier (all p<0.0001). Having insurance (OR 1.378), being NH black (OR 2.458), and being Hispanic (OR 2.980) were associated with reporting fear of receiving bad news as a barrier (all p>0.0001), while older women (OR 0.985, p=0.0001) and women who were screened on the van (OR 0.772, p=0.0026) were less likely to report this concern. Conclusions: Despite provision of free services, cost, fear of procedural pain, and fear of abnormal results remain barriers to mammography utilization among medically underserved women, suggesting the need for more breast health education in this population.