Abstract Background: Among women, breast cancer is the most common noncutaneous cancer and second most common cancerous cause of death. The American Cancer Society recommends that all healthy women over age 40 have a mammogram annually because early detection and treatment of tumors has been associated with a 15% decrease in breast cancer mortality. African American women have higher mortality rates than white women and, in general, uninsured women have low rates of screening. To increase screening rates, mobile mammography has been implemented in many cities. Previous studies have investigated women’s self-reported adherence to screening guidelines at the time of participation in mobile mammography, but no study has examined if women use it as an annual screening tool. Objective: The purpose of this study was to determine if women are using mobile mammography vans as their established source of medical care for breast cancer screening and the factors that predict repeat visits to these vans. Methods: A prospective cohort study was conducted from 2006 to 2013 in which 8450 women who received a mammogram as part of Siteman Cancer Center’s Breast Health Outreach Program responded to surveys and provided access to their clinical records. Only visits on the mammography van were included. The predictor variables explored in this study were: urban status, insurance coverage, age group, race, marital status, mammography experience at baseline visit, employment status, and year of screening. Data were analyzed using chi-square tests, logistic regression, and negative binomial regression. Results: Among the study participants, 25.3% (N=2134) had multiple visits to the mobile mammography van. Of these women, 57.2% had good mammography experiences at baseline, 48.2% were from urban settings, 70.6% were uninsured, 51.2% were ages 50-65, 69.7% were Black, 76.4% were not currently married, and 63.3% were unemployed. Women who were ages 50-65, uninsured, or Black had a higher odds of a repeat visit to the mobile mammography van compared to women who were ages 40-50, insured, or White (OR=1.135, 95% CI: 1.013-1.271; OR=1.302, 95% CI: 1.146-1.479; OR=1.281, 95% CI: 1.125-1.457), respectively. However, the odds of having a repeat visit to the van was lower among women who reported a rural zip code or were unemployed compared to women who provided a suburban zip code or were employed (OR=.503, 95% CI: .411-.616; OR=.868, 95% CI: .774-.972), respectively. Conclusion: This study has identified key characteristics of women who are either more or less likely to use mobile mammography vans as their primary source of medical care for breast cancer screening and have repeat visits. It is important that mobile mammography is maintained and remains easily accessible to women who continuously use the service. Further research should be done to discover ways to make mobile mammography a more effective resource for those more likely to use it for routine screening. Citation Format: Bettina F Drake, Salmafatima S Abadin, Sarah Lyons, Su-Hsin Chang, Lauren T Steward, Susan Kraenzle, Melody S Goodman. Mammograms on-the-go: Predictors of repeat visits to mobile mammography vans in St. Louis, Missouri [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P1-11-06.