Sexual assault, particularly rape and defilement, is a global public health problem. Vihiga County, with a high HIV/AIDS prevalence, reports high rates of these crimes. There is high HIV transmission risk after rape, necessitating HIV Post-Exposure Prophylaxis (PEP) use. However, most victims don’t seek or complete the treatment. This study in Vihiga County, Kenya assessed the barriers to HIV PEP adherence among victims of rape and defilement. Accordingly, the study endeavored to establish and compare the prevalence of rape and defilement and PEP adherence rates among victims within different age groups. The research used a cross-sectional design at three healthcare facilities in Vihiga County: Vihiga County Referral Hospital, Hamisi Sub-county Hospital, and Emuhaya Sub-county Hospital, focusing on victims seeking care in 2021 (January- December). Purposive and cluster sampling techniques were used to select the participants. Data collection involved interviews with healthcare providers and a review of medical records. Analysis methods included thematic analysis, linear and multinomial logistic regression. Result presentation was through frequency tables and percentages. The study revealed a defilement prevalence of 75.5% and a rape prevalence of 24.5%. Notably, defilement was most prevalent among individuals aged 12-17, while rape had a higher prevalence in the 18-49 age group. The age group 12-17 exhibited the lowest PEP completion rate at 14.6%, contrasting with the 60% completion rate observed in the 50+ age group. Linear regression analysis suggested no significant association between age and PEP completion (p = 0.361), indicating that age alone may not determine PEP adherence among victims of rape and defilement. Positive associations were identified between PEP adherence and factors such as drug side effects, pill burden, and lost follow- up (p < 0.001). Barriers to adherence included side effects, pill burden, stigma, lack of support, and service coordination issues. Adolescents and school-going children were identified as being at higher risk of both defilement and PEP non-compliance. With a sample size exceeding expectations at 102 cases, the study signifies its potential generalizability. The findings contribute to academic discourse and offer actionable insights for policymakers, healthcare providers, and support organizations. Recommendations include enhancing post-rape care and PEP awareness in schools and communities, as well as developing milder-side-effect PEP regimens, ideally a single- dose option. Ultimately, the study aims to benefit individuals in Vihiga County by improving public health outcomes and the overall well-being of the community.