Abstract Our objective was to evaluate the liver toxicity of antiretroviral regimens including fosamprenavir plus ritonavir (FPV/r) 1400/100 mg once daily (QD) in HIV/hepatitis C virus (HCV)-coinfected patients. This was a prospective cohort study that included 117 HIV/HCV-coinfected patients who started FPV/r 1400/100 mg QD-based antiretroviral therapy (ART) and who neither had received a previous antiretroviral regimen containing FPV nor had a past history of virologic failure while receiving protease inhibitors (PI). The primary end point of the study was the occurrence of grade 3-4 liver enzymes elevations (LEE) within 1 year after starting FPV/r QD. Factors potentially associated with grade 3-4 LEE, including baseline liver fibrosis, were analyzed. Eleven (9%) patients had a grade 3-4 LEE during the follow-up, resulting in an incidence of severe liver toxicity of 9% (95% confidence interval 4.1-14.6%). None of these cases led to FPV/r discontinuation. Baseline liver fibrosis could be assessed in 97 (83%) patients. Six of 71 patients (8%) with significant fibrosis had a grade 3-4 LEE versus 2 of 26 (8%) without significant fibrosis (p=1.0). Twenty (21%) patients had cirrhosis at baseline. There were no cases of LEE among cirrhotics. In conclusion, the incidence of severe liver toxicity after 1 year of therapy with FPV/r QD-based ART in HIV/HCV-coinfected patients is similar to what has been reported with other boosted PIs. In addition, the presence of significant fibrosis or cirrhosis was not associated with the emergence of liver toxicity. Thus, ART regimens containing FPV/r QD may be considered safe in HIV/HCV-coinfected patients, including those with cirrhosis.