The hepatotoxicity of highly active antiretroviral therapy (HAART) could enhance liver fibrosis in HIV/Hepatitis C virus (HCV)-coinfected patients. Moreover, HAART-related immune restoration could lessen HCV-associated liver damage. The data on the effect of protease inhibitors (PI) on liver fibrosis are scant and contradictory. No information is available on the relationship between non-nucleoside analogue therapy and liver fibrosis in co-infected patients.To investigate the associations between the use of different antiretroviral drugs and the liver fibrosis in patients with HIV and HCV infections.Cross-sectional study.All HIV/HCV co-infected patients with an available liver biopsy and known or estimated duration of HCV infection seen at a Infectious Diseases Unit were included in the study. The fibrosis stage and the fibrosis progression rate were evaluated.The inclusion criteria were fulfilled by 152 patients. Age at HCV infection < 20 years [adjusted odds ratio (AOR), 0.39; 95% confidence interval (CI), 0.19-0.82], PI-based HAART (AOR, 0.39; 95% CI, 0.19-0.78) and nevirapine-based HAART (AOR, 2.56; 95% CI, 1.02-6.58) were associated with fibrosis stage >or= F3. The variables associated with fibrosis progression rate > 0.2 units/year were age at HCV infection < 20 years (AOR, 0.23; 95% CI, 0.1-0.52), CD4 cell counts < or = 250 x 10/l at liver biopsy (AOR, 2.8; 95% CI, 1.1-7.1), PI-based HAART (AOR, 0.39; 95% CI, 0.2-0.8) and nevirapine-based HAART (AOR, 3.82; 95% CI, 1.9-7.6).HAART regimens including nevirapine are associated with faster liver fibrosis progression in HIV-infected patients with chronic hepatitis C. In contrast, patients on PI as the backbone of potent antiretroviral therapy are more likely to show less liver fibrosis.