BACKGROUND: Most antiretroviral drugs are metabolized by the liver; hepatic disease or liver damage as a result of hepatitis C virus (HCV) could impair this metabolism leading to an increased risk of drug toxicity. This study aimed to determine the risk of antiretroviral drug discontinuation among HCV/HIV coinfected patients. METHODS: EuroSIDA patients taking combination antiretroviral therapy were included. Poisson regression identified factors associated with antiretroviral treatment discontinuation. RESULTS: A total of 9535 HIV-positive patients with known HCV status were included (6939 HCVAb-negative; 2596 HCVAb-positive at baseline). Viremic HCV infection was associated with a 44% increased risk of antiretroviral drug discontinuation compared with aviremic infection [adjusted incidence rate ratio, aIRR: 1.44 (95% confidence interval, CI 1.22-1.69)]; this relationship was largest among nonnucleoside reverse transcriptase inhibitors [aIRR: 1.59 (95% CI 1.18-2.14)]. In the subset of 935 HIV-positive patients also HCV-positive or HBV-positive with plasma hyaluronic acid measured, hyaluronic acid more than 100 ng/ml was associated with a 37% increased risk of antiretroviral drug discontinuation [aIRR: 1.37 (95% CI 1.08-1.73) vs. hyaluronic acid ≤100 ng/ml] and the effect of HCV viremia became nonsignificant; the largest drug association was seen for protease inhibitors [aIRR: 1.40 (95% CI 1.04-1.89)]. CONCLUSION: HCV viremia and high levels of hyaluronic acid predict antiretroviral drug discontinuation. Evidence was also found to suggest a link between impaired liver function and protease inhibitor toxicity.