Globally, injection drug use continues to account for a substantial proportion of HIV infections. There have not, however, been any evidence-based reviews of the barriers and facilitators of HIV treatment among injection drug users. For this review, published studies were extracted from nine academic databases, with no language or date specified in the search criteria. Existing evidence demonstrates that, although injection drug users often have worse outcomes from HIV treatment than non-injection drug users, major antiretroviral-associated survival gains still have been observed among this population. Inferior outcomes are explained by a range of barriers to antiretroviral access and adherence, which often stem from the negative influences of illicit drug policies, as well as issues within medical systems, including lack of physician education about substance abuse. Evidence demonstrates that several under-utilized interventions and novel antiretroviral delivery modalities have helped to greatly address these barriers in several settings, and there is sufficient evidence to support immediate scale-up of these programmes. These interventions include coupling antiretroviral therapy with opioid substitution therapies as well as directly administered antiretroviral therapy programmes. Of particular interest for future evaluation is the coupling of HIV treatment programmes within comprehensive services, which also provide low-threshold (harm reduction) HIV prevention programmes. Scale-up of evidence-based HIV treatment and prevention to injection drug users, however, will require increasing political will among both national policy-makers and international public health agencies.