Applying life course theory, this study examined the direct and indirect effects of adverse childhood experiences (ACEs) on the risk of contracting sexually transmitted diseases (STDs), mediated by early sexual activity (first sexual experience before age 15), number of lifetime sex partners, and mental health problems. The link between ACEs and mental health on college students' sexual risk is still understudied. Using cross-sectional data from a sample of 327 college students in Sierra Leone, this study tested the hypothesized mediation model using structural equation modeling analysis. The results showed that ACEs significantly increased sexual risks. Specifically, ACEs increased the risk of early initiation of sexual activity and the number of lifetime sex partners, which in turn increased the risk of STDs. Furthermore, ACEs significantly predicted negative mental health and were significantly associated with an increased risk of STDs. Effective future intervention strategies should include health education programs to address the lifelong effects of ACEs and mental health treatment.