OBJECTIVES:To investigate mental health effects associated with exposure to trauma in Rwanda during the 1994 genocide period, and over the lifetime, in Rwandan men and women aged 20-35 years. SETTING:This was a cross-sectional population-based study conducted in the southern province of Rwanda. Data was collected during December 2011 to January 2012. PARTICIPANTS:A total population of 917 individuals were included, 440 (48%) men and 477 (52%) women aged 20-35 years. Number of households for inclusion in each village was selected proportional to the total number of households in each selected village. The response rate was 99.8%. Face-to-face interviewing was done by experienced and trained clinical psychologists, following a structured questionnaire. RESULTS:Women were slightly less exposed during the genocide period (women 35.4% and men 37.5%; p=0.537), but more women than men were exposed to traumatic episodes over their lifetime (women 83.6%, n=399; men 73.4%, n=323; p<0.001). Current major depressive episodes (MDE) were twice as prevalent in women as in men. Traumatic episodes experienced in the genocide period severely affected men's current mental health status with relative risk (RR) 3.02 (95% CI 1.59 to 5.37) for MDE past and with RR 2.15 (95% CI 1.21 to 3.64) for suicidality. Women's mental health was also affected by trauma experienced in the genocide period but to an even higher extent, by similar trauma experienced in the lifetime with RR 1.91 (95% CI 1.03 to 3.22) for suicidality and RR 1.90 (95% CI 1.34 to 2.42) for generalised anxiety disorder, taking spousal physical/sexual violence into consideration. CONCLUSIONS:Depression, post-traumatic stress disorder, anxiety and suicidal attempts are prevalent in Rwanda, with rates twice as high in women compared with men. For women, exposure to physical and sexual abuse was independently associated with all these disorders. Early detection of gender-based violence through homes and community interventions is important.