The nature, context and frequency of use of various licit and illicit non-injection drugs associated with an elevated risk of HIV infection. Beyond HIV, a high proportion of HIV-infected IDUs are co-infected with HCV (hepatitis C virus). In this review, we provide a brief review of the epidemiology of these problems, discuss behavioral interventions that can reduce ongoing high risk behaviors among HIV-seropositive IDUs and MSM-DUs, and review the literature which has evaluated their effectiveness. The majority of these interventions have focused on HIV-seronegative heterosexuals and therefore need to be considered in this larger context; however, where possible we discuss the potential impact of these interventions among HIV-seropositive persons. In addition, we briefly discuss interventions which have the potential to simultaneously reduce ongoing transmission of both HIV and HCV. Finally, given the dearth of information on the effectiveness of behavioral interventions in reducing the burden of the HIV and HCV epidemics among persons already infected with either or both viruses, we describe some newer, promising interventions and offer suggestions for future studies.