BACKGROUND: In Rwanda, despite significant political achievements in women's empowerment and efforts to eliminate child sexual abuse, the rate of teenage pregnancy remains high. Increased access to and use of contraceptive methods could reduce the rates of teenage pregnancy and HIV infection. OBJECTIVES: The study aimed to identify sociodemographic characteristics of secondary school teenagers, factors influencing their access to contraceptive methods and HIV preventive services, the components of the theory of planned behaviour that underlie teenagers' access to these services, and propose strategies for improvement. METHODS: A cross-sectional design was used in this study. A multistage sampling strategy with a simple random technique was employed to select 374 female students as participants. Data were collected using a pretested questionnaire composed of closed-ended questions with Likert scale constructs based on the Theory of Planned Behavior. Descriptive statistics, bivariate analysis, and multivariable logistic regression were conducted. RESULTS: A multiple logistic regression analysis shows that participants aged 18-20 are more than twice as likely to use contraceptive methods or HIV preventive measures compared to those aged 13-15 (OR = 2.876, P = 0.041, 95% CI = 1.974-4.052). Urban participants are also more than twice as likely to use contraceptives or HIV preventive methods compared to those whose schools are in rural areas (OR = 2.333, P = 0.037, 95% CI = 1.261-4.316). Female students in Senior 6 are more than three times as likely to use contraceptive methods or HIV preventive measures compared to those in Senior 1 (OR = 3.444, P = 0.032, 95% CI = 2.544-6.884). Participants who intend to have sex at an older age had a 24.9% reduction in the odds of using a contraceptive method or HIV preventive measures (OR = 0.751, P = 0.033, 95% CI = 0.352-0.977). Friends of respondents also influence contraceptive use (OR = 0.611, P = 0.043, 95% CI = 0.252-0.917). Participants with contraceptive knowledge are three times more likely to use contraceptives or HIV preventive methods compared to those with less contraceptive knowledge (OR = 3.096, P = 0.011, 95% CI = 1.150-6.803) CONCLUSION: Area of residence, age, friendships, and knowledge of contraceptive methods and HIV preventive measures are the determinants underlying early sexual activity among teenagers. One of the biggest challenges is the level of sex education, which remains a taboo topic in Rwandan culture. It is still difficult for parents to discuss sex directly with their children. We recommend further studies to focus on teenage non-scholars while conducting similar research.