Hepatitis B infection is hyperendemic in the adult population of Niue. In order to determine the age at which infection is acquired and the contribution of vertical and horizontal transmission, the sera from 1055 children were tested for markers of hepatitis B infection. Eleven percent (11.0%) were found to be carriers of hepatitis B surface antigen (HBsAg) and a further 33.6% had antibody to hepatitis B surface antigen (anti-HBs). While less than 15% of the population were infected before the age of two years, these children had the greatest risk of becoming chronic carriers. The simplest method of controlling hepatitis B infection in Niue would be to immunise all newborn babies.