We present findings of a process evaluation of a Comprehensive Sexuality Education (CSE) program for young adolescents in 15 schools in South-Western Uganda.Using the Medical Research Council (UK) framework for process evaluation and the European Expert Group guidance on evaluation of sexuality education programs, we conducted a mixed methods study comprised of a review of relevant implementation documents, qualitative interviews(16), and focus group discussions(4) distributed among 50 participants including pupils, teachers, student educators and parents.Delivery of the anticipated 11 CSE lessons occurred in all target schools with moderate to high pupil attendance, however the duration of sessions was often shorter than planned. Facilitating factors for implementation included establishment of a community advisory board, use of multiple interactive delivery methods and high acceptance of the program by key stakeholders. Socio-cultural norms, geographical access, time constraints and school related factors were barriers.It was feasible to implement a contextually adapted CSE program for young adolescents in schools successfully with overall high acceptance by key stakeholders. Proper coordination of school activities with the program, ensuring linkages of the school based CSE program with community support systems for adolescent SRH and addressing socio-cultural impedances could be beneficial.