Here we present results from a process evaluation of a peer-led HIV prevention intervention. The Risk Avoidance Partnership, conducted from 2001 to 2005, trained active drug users to be peer health advocates (PHAs) to provide harm reduction materials and information to their peers. Results indicate that PHAs actively conducted harm reduction outreach both when partnered with staff and on their own time. Although PHAs conducted most of their outreach in public locations, they also provided drug users with harm reduction materials at critical moments in places where HIV risky behaviors were likely to occur. PHAs were credible and trusted sources of information to their drug-using peers who sought PHAs out for HIV prevention materials. Process evaluations of successful HIV prevention interventions are necessary to understand how and why such interventions work for further intervention refinement.