Recruitment of people who use drugs (PWUD) for HIV-related research has been undertaken since early in the epidemic. In early studies, recruitment was often performed by outreach workers with familiarity with the target population, who distributed risk reduction materials, and administered the surveys being conducted on drug use and risk behaviors. The evolution of effective treatments for HIV has provided opportunities for PWUD to participate in biobehavioral studies testing the efficacy of medical treatment advances and exploring the underlying biomedical basis for prevention and treatment efforts. Recruitment for these studies has led to new challenges for outreach workers and institutions conducting this research. PWUD, particularly those from race/ethnic minority populations, have had lower rates of engagement in HIV care and have been underrepresented in HIV/AIDS medical studies. To address these health disparities, enhanced efforts are needed to increase their participation in biomedical studies. This article examines the challenges identified by experienced outreach workers in recruiting PWUD for HIV-related biomedical studies, including individual (participant)-, institutional-, and recruiter-level challenges, and provides recommendations for addressing them.