Posttreatment exacerbation of hepatitis B virus (HBV) infection in long-term HBV trials of emtricitabine occurred in 23% of patients. Development of antibody to hepatitis e antigen did not prevent hepatic flare. One patient with marked bridging fibrosis required liver transplantation. Patients with advanced liver disease are at risk for hepatic flare with decompensation if active treatment is withdrawn (e.g., when highly active antiretroviral treatment is modified).