The rare emergence of hepatitis B virus (HBV) reactivation among hepatitis C virus (HCV)-infected patients receiving direct-acting antiviral (DAA) therapy raises questions about how many HCV-infected patients have active, past, or latent/occult HBV co-infection, and their DAA treatment experience1–3 We sought to characterize these factors, including possible post-DAA reactivation, among HCV patients in the Chronic Hepatitis Cohort Study (CHeCS), a “dynamic” observational study conducted at 4 large integrated U.S.