 Human immunodeficiency virusHepatitis B virus HIVHBV co-infections are frequently observed due to shared routes of transmission, with reported figures indicating 6-9 of HIV-infected individuals in developed countries are chronically infected with HBV. HIV infection impacts on the natural progression of HBV infection, increasing levels of HBV replication and the risk of liver-associated mortality. Liver diseases associated with HBV are affected by the antiviral drugs used for HIV infection toxic side effects, the current immune function in the patient, by improvements in the immune system brought about by control of the HIV infection, and by the development of resistance to the antiviral agents used for both the hepatitis B and the HIV infection. Co-infection with HBV increases the risk for hepatotoxicity in those individuals receiving highly active antiretroviral therapy HAART for their HIV infection. 