BACKGROUND & AIMS: Patients with acute hepatitis C virus (HCV) infection who receive treatment achieve high rates of sustained virologic response (SVR), but few studies have examined outcomes among injecting drug users (IDUs). We evaluated the efficacy of treatment of recent HCV infection in IDUs with acute and early chronic HCV. METHODS: We analyzed data from the Australian Trial in Acute Hepatitis C-a prospective study of the natural history and treatment outcomes of patients with recent HCV infection. Participants eligible for the study had their first anti-HCV antibody-positive test result within the past 6 months and either acute clinical HCV within the past 12 months or documented anti-HCV seroconversion within 24 months. Participants with HCV received pegylated interferon-alfa-2a (180 microg/wk, n = 74); those with HCV/human immunodeficiency virus (HIV) co-infection received pegylated interferon-alfa-2a (180 microg/wk) with ribavirin (n = 35) for 24 weeks. RESULTS: From June 2004 to February 2008, 167 participants were enrolled in the Australian Trial in Acute Hepatitis C; 79% had injected drugs in the previous 6 months. Among 74 with only HCV, the SVRs were 55% and 72% by intention-to-treat and per-protocol analysis, respectively. In multivariate analyses, baseline factors independently associated with lower SVR included decreased social functioning and current opiate pharmacotherapy. Adherent participants had higher SVR rates (63% vs 29%; P = .025). Of the 35 participants with HCV/HIV co-infection, the SVRs were 74% and 75% by intention-to-treat and per-protocol analysis, respectively. CONCLUSIONS: Treatment of recent HCV infection among IDUs, including those with HIV co-infection, is effective. Strategies to engage socially marginalized individuals and increase adherence should improve treatment outcomes in this population.