Potentially eligible patients will be anti-HCV antibody-positive and have detectable serum or plasma HCV RNA. Patients can have any HCV genotype; they also can be antiviral treatment-naïve or have a history of either nonresponse or relapse to previous antiviral therapy. Patients can roll over directly from current interferon (IFN) therapy into registry Infergen therapy, but the average washout period will be <1 month. Rollovers will occur after 4, 12, or 24 weeks of IFN therapy. Patients coinfected with HBV or HIV can be included in the registry.