HIV-infected children had a lower seroconversion rate to hepatitis B immunization and a more rapid antibody decline when compared to healthy children. Whether re-immunization or additional booster dose is necessary after immune recovery remains unknown. This study was conducted to determine the prevalence of hepatitis B virus protective antibody in HIV-infected children with immune recovery after highly active antiretroviral therapy (HAART). Serum hepatitis B viral markers were measured. An antibody level of > or =10 mIU/mL was defined as a protective antibody level. Only one out of 69 children (1%) had a protective antibody level. We concluded that despite the history of hepatitis B immunization and despite evidence of immune recovery after HAART, most HIV-infected children are still susceptible to HBV infection.