Purpose: This paper explores "lessons learned" resulting from a process evaluation of a peer-led HIV/AIDS prevention programme targeting street children and youth in urban Uganda. The purpose was to explore aspects of implementation that either enhanced or hindered the effectiveness of the peer educator (PE) role. Design/methodology/approach: The process data derive from three reviews conducted throughout the project lifespan. The reviews engaged participatory evaluation methods such as focus groups (four) and workshops (three), as well as drawing on monitoring data such as activity evaluations. Findings: The street youth in this project made effective peer educators. We suggest that letting the target group choose their peers and focusing on street youth undergoing rehabilitation engendered ownership of PEs by the target group and accountability among PEs themselves. The role was highly coveted and the PEs became powerful role models. The most useful work of the PEs lay in helping their peers to leave the risky environment of the streets, hence reducing their vulnerability to HIV/AIDS. By defining the role broadly and situating peer education activities within a broader strategy of capacity building and advocacy, we were able to remain sensitive to the context in which street youth make "choices" about their sexual behaviour. Originality/value: This paper contributes significantly to our understanding of the effective implementation of the PE method in this setting. It will be particularly helpful to practitioners in the design stage of similar peer-led programmes. (Contains 4 notes.)