Hepatitis C virus (HCV) infection is highly prevalent and is associated with substantial morbidity and mortality among persons infected with the human immunodeficiency virus (HIV). We compared the efficacy and safety of pegylated interferon alfa-2a (peginterferon alfa-2a) plus either ribavirin or placebo with those of interferon alfa-2a plus ribavirin for the treatment of chronic HCV infection in patients who were also infected with HIV.