The natural history of HBV is known to be complicated by HIV-co-infection. In contrast, the effect of HBV on the outcome of patients infected with HIV-1 is controversial. Some cohort studies from the pre-HAART era described a more rapid progression to AIDS in patients carrying antibodies to the core-antigen or having chronic HBV infection, but post-HAART studies did not detect any impact of HBV co-infection on HIV-disease progression. Similarly, studies assessing the impact of HCV on progression of HIV-disease delivered conflicting results. In the Swiss cohort study, the presence of HCV was independently associated with an increased risk of progression to AIDS and death. Subsequent studies, however, did not find any difference in survival. Most interestingly, the EuroSIDA cohort analysis found no difference between HCV-positive and HCV-negative HIV-patients starting HAART in the time needed to decrease viral loads to less than 400 copies as well as in the time needed to increase CD4-counts by 50%. In summary, there are no major differences in HIV-related mortality between hepatitis B or C co-infected individuals and patients infected with HIV alone, particularly if antiretroviral treatment is given. There is, however, an increased risk of liver disease related morbidity and mortality as well as more hepatoxicity under antiretroviral treatment regimens.