Hepatitis C virus (HCV) and human immunodeficiency virus (HIV) share the same routes of transmission, which explains the high rate of HCV and HIV coinfection (approximately 9%). HIV/HCV coinfection leads to high rates of indeterminate recombinant immunoblot assay patterns and seroreversion; high levels of viral replication; and a more severe histopathologic course. By contrast, HCV infection does not seem to accelerate the progression of HIV infection. Interferon alpha (IFN-alpha) in coinfected patients leads to a similar rate of primary responses, but sustained responses are less frequent. The potential severity of hepatitis C virus infection evidences the need for early diagnosis. Liver biopsy should be performed for all HCV RNA-positive patients in order to evaluate the activity of the liver disease. Given the poor efficiency of IFN-alpha in terms of sustained response in HIV-infected patients, reinforced therapeutic procedures (long-term administration of IFN-alpha or combined ribavirin/IFN-alpha) should be proposed, at least for those patients with severe liver disease.