HIV-infected people who inject drugs (PWID) have low uptake of HIV services, increasing the risk of transmission to uninfected injection or sexual partners and the likelihood of AIDS-related deaths. HPTN 074 is a vanguard study assessing the feasibility of an integrated intervention to facilitate treatment as prevention to PWID in Indonesia, Ukraine, and Vietnam. We describe barriers to and facilitators of ART uptake and adherence among PWID. We conducted in-depth interviews with 62 participants, including 25 providers and 37 PWID at baseline across all sites. All interviews were recorded, transcribed, translated into English and coded in NVivo for analysis. Matrices were developed to identify emergent themes and patterns. Overall, differences between provider and PWID perspectives were greater than differences in cross-site perspectives. Providers and PWID recognized clinic access, financial barriers, side effects, and lack of information about HIV testing and ART enrollment as barriers to ART. However, providers tended to emphasize individual level barriers to ART, such as lack of motivation due to drug use, whereas PWID highlighted health systems barriers, such as clinic hours and financial burden, fears, and side effects. Providers did not mention stigma as a barrier though their language reflected stereotypes about drug users. The differences between provider and PWID perspectives suggest a gap in providers' understanding of PWID. This misunderstanding has implications for patient-provider interactions that may affect PWID willingness to access care or adhere to ART. Lessons learned from this study will be important as countries with a significant HIV burden among PWID design and implement programs to engage HIV-infected PWID in care and treatment.