About 30% of HIV-positive individuals are concomitantly infected with HCV within the United States and Europe. Approximately 50 to 90% of persons who acquired HIV from injecting drugs are co-infected with HCV In these dually infected individuals the presence of each viral infection may impact the natural course of the other one, and worsening of associated liver disease and complications within this population are frequent. The management of chronic hepatitis C (cHC) in HCV-HIV-co-infection has become a major challenge, as possible interactions with antiretroviral therapy (ART), increased risk of special side effects, as well as compromises in adherence of patients, who already take several drugs, have to be taken into account. Treatment strategies to fight HCV-infection have been essentially ameliorated during the past three years in using pegylated interferon alpha (PegIFN alpha) combined with ribavirin (Rbv). There is hope that the beneficial therapeutic outcome in HCV-mono-infected individuals may be at least partly translated into successful treatment of dually infected patients too. However, the stepwise amelioration of therapeutic options and strategies does actually not yet result in equal anti-HCV response rates for co-infected compared to HCV-mono-infected persons. The 1(st) International Workshop on HIV and Hepatitis Co-infection 2004, was initiated to face the severe clinical problems which arise from viral hepatitis and HIV dual infection. The organising committee was headed by J.K. Rockstroh, University of Bonn, Germany, as chair and M. Sulkowski, John Hopkins University, USA, as co-chair of the meeting, in which more than 300 researchers and physicians from various European and US locations participated. This report summarizes some results on epidemiology, pathogenesis, viral interactions, and treatment of chronic hepatitis C in HIV-infected individuals.