Intravenous drug use is a major international health problem. The transmission of HIV through sharing syringes or needles during drug use is an important part of this problem. Injection drug users (IDUs) also engage in high-risk sexual behaviour which facilitates the transmission between different groups. In this article, we present a global perspective of injection drug use in relation to HIV. There are 16 million IDUs worldwide, of whom an estimated 3 million are infected with HIV. The prevalence of HIV among IDUs varies greatly between countries as well as within them. There are intervention programmes to prevent HIV transmission via drug use such as needle and syringe exchange programmes (NSPs) and opioid substitution therapy (OST). These programmes are effective for preventing HIV transmission, provided that their implementation is adequate. 80% of the countries provide NSPs, 65% also provide OST. The coverage of these services is nevertheless insufficient to have an impact on the transmission of HIV.