People who inject drugs (PWID) are at higher risk for acquiring HIV infection than the general population in many countries. Injecting drug use is present in 148 countries including a wide array of low and middle income countries where HIV incidence is growing in recent years - even as it declines elsewhere. This study was undertaken as the third of a series of three economic analyses examining the global epidemics of HIV/AIDS in vulnerable populations. Informed by a critical review of epidemiological evidence and the most recent analyses of intervention efficacy, this work modeled the costs...