There is very little information about hepatitis B virus (HBV) infection in children after liver transplantation. This is the first report of the addition of famciclovir in a child who developed lamivudine resistance. A 5-year-old boy who was serum HBsAg-negative and was not vaccinated against HBV underwent living-related liver transplantation for fulminant hepatitis A. The donor was his mother, who was serum HBcAb-positive. No immunoprophylaxis was administered. HBV infection developed after 18 months and was treated with 3 mg/kg daily of lamivudine. Serum alanine aminotransferase normalized and HBV DNA load decreased significantly. Sixteen months later, lamivudine resistance developed; a mutation (M552I) was confirmed by sequencing through the YMDD locus of the HBV polymerase gene. The addition of 750 mg daily of famciclovir led to seroconversion and the disappearance of serum HBV DNA. Lamivudine in combination with famciclovir might be a therapeutic option for HBV reinfection after liver transplantation, also in children. Suppression of viral replication to undetectable values is possible even in the lamivudine-resistant mutant.