Study P05063 is a 3-year long-term follow-up (LTFU) study in participants previously treated with boceprevir (BOC) or narlaprevir (NAR) in a Phase 1, 2, or 3 clinical study. Participants will be followed for up to 3.5 years after the end of their participation in the treatment protocol to document maintenance of the antiviral response (for sustained responders) and to characterize the long-term safety after use of this therapeutic regimen. LTFU procedures include collection of plasma samples for measuring Hepatitis C Virus ribonucleic acid (HCV-RNA) by polymerase chain reaction (PCR) and HCV sequence analysis. No drug therapy will be administered as part of this study.