The age specific prevalence of hepatitis B surface antigen and antibody was studied among a random sample of Nauruans over the age of 10 years. Overall, 79% of subjects showed evidence of past infection with hepatitis B virus with the highest prevalence among young people. While there was no difference in the infection rate between males and females, the carrier rate in males was 50% higher. In both sexes the carrier rate declined with increasing age. Significant differences in carrier rates were detected among people living in different parts of the island.