Hepatitis C virus (HCV) infection occurs in about one-third of HIV-seropositive patients and in about 90% of HIV-positive drug abusers. After the introduction of highly active antiretroviral therapy (HAART) and the subsequent reduction in mortality from opportunistic infections, HCV-related liver failure has become a frequent cause of death in HIV-positive patients. In HIV-seropositive patients, the course of HCV infection is accelerated and there is evidence that HCV is an important factor for HIV progression. Consequently, it is important to establish the appropriate treatment for HCV infection in HIV-seropositive patients. This review examines the epidemiology, physiopathology, diagnostics and treatment of HIV/HCV coinfection with particular regard to the impact of HAART.