Our objective was to estimate the prevalence of HCV and HBV co-infection among HIV-infected adults in France and describe the epidemiological characteristics of co-infected patients and their clinical management. A one-day national cross-sectional survey was conducted in 2004. A random and proportional probability sample design was used, based on the number of AIDS cases reported since 1999 by hospital wards. Weighted estimations were computed. HIV-infected adults (out/in-patients) were included after consent. Data were collected on demographic criteria, HIV, HCV and HBV infections, as well as on antiviral therapies. Overall, 1849 HIV-infected patients were included. The prevalence of anti-HCV or HCV RNA positivity (HCV co-infection) was 24.3% [95% confidence interval (CI): 21.3-27.6] and varied from 3.1% in men who had sex with men to 92.8% in injecting drug users (IDUs). The prevalence of positive HCV RNA was 17.0% [95% CI:14.7-19.4]. The prevalence of HBs antigen (Ag) or HBV DNA positivity was 7.0% [95% CI: 5.9-8.1] and varied with the continent of birth from 2.1% in Northern Africa to 10.8% in sub-Saharan Africa. The prevalence of HIV-HCV-HBV co-infection was 1.6% [95% CI: 1.0-2.4], mostly IDUs (83.3%). A severe liver disease (cirrhosis or hepatocellular carcinoma) was diagnosed in 24.7% of the positive HCV RNA patients. This study confirmed the burden of HCV infection in French HIV-infected patients and described for the first time in France the epidemiological characteristics of HIV-HBV co-infection. Furthermore, it stresses the severity of liver disease related to HCV in HIV-infected population.