Objective: To describe and estimate the availability of antiretroviral treatment (ART) to injecting drug users (IDUs) in developing and transitional countries. Methods: Literature review of grey and published literature and key informants' communications on the estimated number of current/former injecting drug users (IDUs) receiving ART and the proportion of human immunodeficiency virus (HIV) attributed to injecting drug use (IDU), the number of people in ART and in need of ART, the number of people living with HIV/acquired immunodeficiency syndrome (AIDS) (PLWHA) and the main source of ART. Results: Data on former/current IDUs on ART were available from 50 countries (in 19 countries: nil IDUs in treatment) suggesting that ~34 000 IDUs were receiving ART by the end of 2004, of whom 30 000 were in Brazil. In these 50 countries IDUs represent ~15% of the people in ART. In Eastern European and Central Asia IDU are associated with > 80% of HIV cases but only ~ 2000 (14%) of the people in ART. In South and South-East Asia there were ~1700 former/current IDUs receiving ART ~1.8% of the people in ART), whereas the proportion of HIV cases associated to IDU is > 20% in five countries (and regionally ranges from 4% to 75%). Discussion: There is evidence that the coverage of ART among current/former IDUs is proportionally substantially less than other exposure categories. Ongoing monitoring of ART by exposure and population subgroups is critical to ensuring that scale-up is equitable, and that the distribution of ART is, at the very least, transparent. (Author' s abstract)