To understand the prevalence and incidence of hepatitis A virus (HAV) infection in Chinese children in Taiwan, we determined the age-specific prevalence of hepatitis A antibodies (anti-HAV) in 823 children, ranging from birth (cord blood) to 19 years of age. The frequency of anti-HAV rose with increasing age with three different slopes, probably reflecting different age-specific incidences: lowest under 4 years of age, intermediate between 4 and 10 years, and highest above 10 years. We obtained follow-up specimens on 618 of the preschool children under 6 years of age. 11 (1.9%) of the 573 without antibodies had seroconversions after an average of 1.9 years of follow-up. The annual incidence was 1.0% and increased with advancing age of the children after infancy. None of the 11 seroconversions had clinical hepatitis. Among the 28 children 1-24 months of age who had antibodies, only 1 was positive on follow-up, reflecting loss of passively acquired maternal antibody in most children.