Because of shared modes of transmission, co-infection with human immunodeficiency virus (HIV) and hepatitis C virus (HCV) is common. Co-infection with HIV increases HCV virus load, liver-related mortality, and the risk of sexual and perinatal transmission of HCV, and it may accelerate HCV disease progression. With combination interferon (IFN)-alpha 2b/ribavirin or pegylated IFN-alpha 2b/ribavirin therapy, long-term remission is possible for HCV-infected patients. Preliminary evidence suggests that the combination of IFN-alpha 2b/ribavirin can achieve similar response rates in HCV/HIV-co-infected individuals with no adverse effect on HIV RNA concentrations. Although adverse effects are more frequent with combination therapy than with IFN-alpha monotherapy, most are manageable. In addition, few instances of drug-drug antagonism have been reported among drugs used to treat each disease, although further study is necessary. Ribavirin-associated hemolytic anemia is a potential problem in a patient population that is already susceptible to anemia but is manageable with recombinant human erythropoietin (epoetin alfa).