Since human immunodeficiency virus (HIV) and hepatitis C virus (HCV) share the same modes of transmission, HIV-HCV co-infected patients are relatively common. Until recently, the clinical course of HCV in co-infected patients was overshadowed by the high morbidity and mortality of HIV disease. Recent reductions in morbidity and mortality among HIV-infected patients due to the advent of highly active antiretroviral therapy (HAART), have contributed to the emergence of HCV as a significant viral pathogen in this population. This article reviews the current evidence on the epidemiology and clinical implications of an interaction between HIV-1 and HCV infections.