Background The world is dealing with a significant socio-economic burden that must be addressed to secure a favourable future.To figure out this problem, there is an urgent need of healthy and well educated adult population to participate effectively in global economy.Indeed, childhood experiences may affect adult health outcome.Responsive caregiving during childhood is associated with good physical and mental health.On the other hand,a strong link was established between Adverse Childhood Experiences (ACEs) and poor adult physical and mental health outcomes.This study assessed the prevalence of ACEs among adult patients with mental disorders admitted to the post-crisis wards at Caraes Ndera Neuropsychiatric Hospital in Kigali, Rwanda. Methodology : This research was developed as a descriptive cross-sectional study that involved a total of 122 patients aged 18 to 64 years.A convenience sampling was used to collect data using the the Adverse Childhood Experiences International Questionnaire (ACE-IQ). Data was analyzed in terms of frequencies and percentages using the Statistical Package for the Social Sciences (SPSS 21.0). Results Initially, 159 participants were invited to join the study, 122 (77%) met the inclusion criteria and voluntarily consented to participate. Of the 122 participants, 43.4% were female, 61% were youth, 67.2% had primary school as the highest level of education and 29.5% did not work during the last 12 months. Having separated/divorced or deceased parents was the most frequent ACE item with 64.8% of participants responding affirmatively. Nearly all (98.4%) participants had at least one ACE and 77.9% had at least 4 ACEs. Conclusions This study on ACEs in Rwandan adults with mental disorders revealed that 98.4% had at least one ACE and almost 80% of the 122 participants had at least 4 ACEs.The findings indicate that there is a significant need to implement interventions necessary for the prevention of ACEs. Such interventions are necessary to mitigate negative effects of ACEs on child development, to increase children’s resiliency and to improve future adult physical and mental health outcomes.