BACKGROUND Patients with chronic hepatitis C virus (HCV) infection experience antiretroviral-associated liver toxicity more frequently than HIV mono-infected persons. Herein, we report the hepatic safety profile of raltegravir in a relatively large group of HIV/HCV co-infected patients, a population that was poorly represented in the registrational studies. METHODS Prospective, observational study of all antiretroviral-experienced HIV-infected patients who initiated raltegravir from January 2006 to January 2009 at a reference HIV clinic. Clinical data, laboratory parameters and liver stiffness measured at baseline, week 4 and every 3 months thereafter were collected. Chronic hepatitis C was defined as positive serum HCV-RNA. Grade 1-4 hepatotoxicity was defined following the AIDS Clinical Trials Group definition for liver enzyme elevations (LEEs). A control group of patients who initiated protease inhibitors (PIs) or non-nucleoside reverse transcriptase inhibitors (NNRTIs) was examined similarly. RESULTS Data from 218 HIV-infected patients on raltegravir were analysed, 126 HIV mono-infected and 92 HIV/HCV co-infected patients. Any degree of LEEs occurred in 10 (7.9%) HIV mono-infected and 23 (25%) co-infected patients (relative risk 3.1; 95% confidence interval 2.9-3.4; P = 0.002). Severe hepatotoxicity (grade 3-4), however, was only seen in 3 (1.4%) patients, all co-infected with HCV. It occurred at months 1, 15 and 15, respectively. In all three subjects other reasons than raltegravir exposure most likely explained LEEs. Multivariate analysis revealed HCV co-infection as the only independent variable associated with any degree of hepatotoxicity on raltegravir (P = 0.03). Finally, the rate of LEEs in patients on raltegravir was lower than in those who were treated with PIs or NNRTIs. CONCLUSIONS LEEs are less frequent in patients treated with raltegravir than with other antiretroviral drug classes. However, HIV/HCV co-infected patients treated with raltegravir experienced LEEs more frequently than HIV mono-infected persons. In this series, LEEs in patients treated with raltegravir were uniformly mild and no cases of grade 3-4 hepatotoxicity could be directly attributed to the drug. These results reinforce the overall hepatic safety profile of raltegravir.