Limited research has been conducted to examine the effectiveness of existing HIV prevention and harm reduction interventions targeted to injection drug-using youth. Moreover, although there are a growing number of needle exchange programs being developed for youth throughout the United States, the effects of these services have yet to be systematically evaluated. This article describes a collaborative evaluation conducted by the Division of Adolescent Medicine, Childrens Hospital Los Angeles, and Clean Needles Now, a needle exchange serving young injection drug users. The evaluation employed a multimethod research design that included both qualitative and quantitative methods. Findings are presented about how a community-based agency’s service delivery philosophy can affect the design and implementation of an evaluation. Lessons learned from this collaborative evaluation are presented, including the potential benefits of incorporating harm reduction principles into research activities. (abstract from the article)