Hepatitis B infection is hyper-endemic in Tonga and 19% of pregnant women test positive for hepatitis B surface antigen (HBsAg). Routine childhood immunization against hepatitis B was introduced in 1989 and the target for elimination was set at <1% HBsAg prevalence in children. A study conducted in 1998, a decade after the introduction of hepatitis B immunization, found the HBsAg prevalence to be 3.8% in pre-school children. The finding resulted in the strengthening of the delivery of hepatitis B vaccine with emphasis on providing the first dose within 24 h after birth. The aim of this study was to measure the impact of improved immunization practices on the prevalence of hepatitis B infection in pre-school children, and to assess the progress towards hepatitis B elimination in Tonga.