Abstract Introduction Human papillomavirus (HPV) surveillance is lacking in Puerto Rico (PR). We aim to estimate the seroprevalence of the HPV types included in the nonavalent vaccine (9vHPV) in women and explore associations. Methodology A population-based cross-sectional study of socio-demographic, clinical [including, sexually transmitted infections (STIs)], and behavioral characteristics of sexually active women (16-64 years) was conducted in PR from 2010-2013. Blood samples from 524/566 (92.6%) HPV unvaccinated women were included in this sub- analysis. Antibody responses to 9vHPV types (HPV-6/11/16/18/31/33/45/52/58) were analyzed using M9ELISA by the U.S. Centers for Disease Control and Prevention (CDC). A self-collected cervical and anal sample from all 524 women were also tested using L1 consensus primer (MY09/MY11) PCR followed by dot hybridization to detect 40 HPV types. Statistical analyses included Pearson’s chi-square and logistic regression models. Adjusted odds ratios (aOR) and 95% confidence intervals (CI) were reported. Results The mean age of participants was 42.4 years ± 0.6 standard deviations (SD), 52.5% were married/cohabited, and 9.7% were uninsured. About half (51.3%) had between 3-9 lifetime sexual partners, 15.9% had history of STIs, and 40.3% had a current anogenital HPV infection. Overall, 65.8% were seropositive to at least one of the 9vHPV types (1.0% to all 9vHPV types), 59.9% to any of the seven oncogenic types (HPV-16/18/31/33/45/52/58) and 49.1% to any of the quadrivalent vaccine (4vHPV) types. The seroprevalence for specific HPV types ranged between 10.7%-28.1% [HPV-33 (10.7%), 11 (11.6%), 45 (11.8%), 58 (15.8%), 18 (18.7%), 31 (25.0%), 6 (26.2%), 52 (26.9%), and 16 (28.1%)]. In bivariate analysis, significant associations between 9vHPV types were observed with marital status, age at sexual debut, lifetime sexual partners, anal sex, history of STIs and anogenital HPV infection (p<0.05). In the multivariate model, divorced/separated/widowed women (aOR: 2.2, 95%CI: 1.2-4.3) had higher odds of seropositivity to any of the 9vHPV types than single women. Women with 3-9 (aOR: 2.4, 95%CI, 1.5-3.8) and with >10 (aOR: 3.1, 95%CI, 1.6-5.8) lifetime sexual partners had higher odds of seropositivity than women with 1-2 partners. Women with a history of STIs (aOR: 2.1, 95%CI, 1.1-4.0) and with an anogenital HPV infection (aOR: 1.9, 95%CI, 1.2-2.9) had higher odds of HPV seropositivity than their counterparts. In this model, no differences were observed by age, education, healthcare coverage, age at sexual debut or anal sex. Conclusion Before implementation of the HPV nonavalent vaccine, the seroprevalence of at least one of the 9vHPV types among women in PR was high (65.8%). However, less than 1% of women were seropositive for all nine HPV types, indicating this population would benefit from HPV vaccine implementation. Acknowledgements Study funded by the National Institute of Allergy and Infectious Diseases Grant (Grant #1SC2AI090922-01) of the National Institutes of Health. Citation Format: Angeline Cruz, Jeslie M. Ramos-Cartagena, Gitika Panicker, Elizabeth Unger, Ana P Ortiz. The seroprevalence of nine human papillomavirus types included in the nonavalent vaccine in unvaccinated women living in Puerto Rico [abstract]. In: Proceedings of the 17th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2024 Sep 21-24; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2024;33(9 Suppl):Abstract nr A112.