BACKGROUND: Age-disparate relationships (ADR) place adolescent girls and young women (AGYW) at higher risk of unprotected sex and HIV infection; few studies have investigated ADR at first sex in sub-Saharan Africa. This study investigates ADR at first sex and its association with reproductive autonomy, reproductive empowerment, contraception coercion, and consent at first sex among female Rwandan youth. METHODS: Cross-sectional data from a randomized trial (n = 5768) of in-school youth ages 12-19 at enrollment were analyzed with focus on those who reported sexual activity (n = 1319). General estimating equation linear models and Poisson models were used to estimate linear coefficients and prevalence ratios (PR), with 95% confidence intervals (CIs) estimated using robust standard errors. RESULTS: Females reported a significantly higher average partner age gap than males by 2.43 years (2.90 years vs. 0.46 years, 95% CI: 2.01, 2.86). Overall, 23.4% (n = 102) of sexually active AGYW engaged in an ADR at first sex. The prevalence of non-consensual first sex was 60% higher among AGYW reporting ADR at first sex compared to AGYW reporting similar-aged partners (adjusted PR = 1.59, 95% CI: 1.25, 2.02). No association was found between ADR at first sex and reproductive autonomy, reproductive empowerment, or contraception coercion. CONCLUSIONS: Our results suggest a high prevalence of sexual violence among AGYW engaging in first sex with an age-disparate partner. However, we did not find evidence that ADR at first sex affects reproductive autonomy or empowerment within the first few years of sexual initiation. Further research is needed to explore the impact of ADR at first sex and longer-term trajectories of sexual behavior, empowerment and autonomy.