Over the past decade, a body of observational research has accrued about the effects of outreach-based human immunodeficiency virus (HIV) interventions for drug users. The authors reviewed the findings related to postintervention behavior changes and integrated findings across studies to provide the best estimate of program impact.|The authors conducted a computerized literature search to locate published accounts of HIV intervention effects on drug users. Thirty-six publications covered outreach-based HIV risk reduction interventions for out-of-treatment injecting drug users (IDUs) and reported intervention effects on HIV-related behaviors or HIV seroincidence. Two-thirds of the publications reported that participation in street-based outr...