In British Columbia, human immunodeficiency virus (HIV)-infected persons eligible for antiretroviral therapy may receive it free but the extent to which HIV-infected injection drug users access it is unknown. To identify patient and physician characteristics associated with antiretroviral therapy utilization in HIV-infected injection drug users. Prospective cohort study with record linkage between survey data and data from a provincial HIV/AIDS (acquired immunodeficiency syndrome) drug treatment program. British Columbia, where antiretroviral therapies are offered free to all persons with HIV infection with CD4 cell counts less than 0.50 x 10(9)/L (500/microL) and/or HIV-1 RNA levels higher than 5000 copies/mL. A total of 177 HIV-infected injection drug users eligible for antiretroviral therapy, recruited through the prospective cohort study since May 1996. Patient use of antiretroviral drugs through the provincial drug treatment program and physician experience treating HIV infection. After a median of 11 months after first eligibility, only 71 (40%) of 177 patients had received any antiretroviral drugs, primarily double combinations (47/71 [66%]). Both patient and physician characteristics were associated with use of antiretroviral drugs. After adjusting for CD4 cell count and HIV-1 RNA level at eligibility, odds of not receiving antiretrovirals were increased more than 2-fold for females (odds ratio [OR], 2.53; 95% confidence interval [CI], 1.08-5.93) and 3-fold for those not currently enrolled in drug or alcohol treatment programs (OR, 3.49; 95% CI, 1.45-8.40). Younger drug users were less likely to receive therapy (OR, 0.47/10-y increase; 95% CI, 0.28-0.80). Those with physicians having the least experience treating persons with HIV infection were more than 5 times less likely to receive therapy (OR, 5.55; 95% CI, 2.49-12.37). Despite free antiretroviral therapy, many HIV-infected injection drug users are not receiving it. Public health efforts should target younger and female drug users, and physicians with less experience treating HIV infection.