This report documents the processes and results of a project that scientifically tested the effectiveness of the participatory approach in defining and addressing the reproductive health concerns of adolescents. The project was conducted in Nepal between 1998 and 2003 and was undertaken jointly by EngenderHealth and the International Center for Research on Women (ICRW), in collaboration with Nepali partners. Although there is an extensive and growing literature on participatory research and design models for youth reproductive health (YRH), there have been no comprehensive evaluations conducted to date on the impact of a participatory process on youth reproductive health in developing country settings. The ICRW-EngenderHealth effort described here aimed to fill this gap through rigorous analysis and evaluation. The project was set up with a quasi-experimental study design utilizing the participatory approach for research, intervention, monitoring, and evaluation at two study sites (one rural and one urban), together with more traditional reproductive health research and interventions at two control sites. An extensive needs assessment was conducted at the study sites using triangulated methodologies, followed by action planning with the community to design the program. At the control sites, a more limited needs assessment was conducted, and based on current knowledge and standard practice in the reproductive health field, a set of three interventions was implemented. These included: 1) adolescent-friendly services; 2) peer education and counseling; and 3) teacher training. (excerpt)