At initiation of this study in 1991, approximately 0.6% of U.S. blood donors were identified as having antibody to the hepatitis C virus (anti-HCV). This represented 72,000 of the estimated 12 million annual U.S. blood donations. By investigating a cohort of anti-HCV positive donors, this study aims to determine: 1) the primary routes of HCV transmission in an asymptomatic donor population; 2) the relationship between anti-HCV and evidence of acute or chronic liver disease; 3) the infectivity of anti-HCV positive individuals as judged by measurement of HCV RNA and by investigation of their sexual partners and prior blood recipients; 4) the chronic consequences of HCV infection. The study does not directly provide treatment for HCV infection. Enrollment is limited to persons identified as anti-HCV positive at the time of blood donation and persons from any source found to have clinical or molecular evidence of acute hepatitis C virus infection. Although the primary goal of this study is to investigate HCV infection and its outcomes, we occasionally encounter blood donors or NIH patients who are infected with HBV or who have HCV-HBV coinfection. We will enroll such patients to better understand HBV infection and to compare outcomes in those who are HCV monoinfected, HBV monoinfected or who have HCV-HBV coinfection.