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INTRODUCTION: Hepatitis A is a vaccine-preventable disease with epidemiology that has changed over the past decades. In Greece, the vaccine has been available and recommended, but no universal mass vaccination has been implemented as yet. OBJECTIVE: We sought to study the seroepidemiology of hepatitis A in Greek children. METHODS: The seroepidemiology of hepatitis A in children 0 to 14 years of age living in Greece was studied. We collected 100 sera per year of age, stratified by geographic region. Demographic data and documented hepatitis A vaccine history was entered into a specially designed anonymous database. Sera were tested for the presence of anti–hepatitis A virus immunoglobulin G antibodies (AxSYM, Abbott Laboratories, Hellas, Greece). RESULTS: Data from 948 children analyzed revealed that 40.7% of the children had received at least 1 dose of hepatitis A vaccine. To date we have examined 498 sera. Among fully vaccinated children who had received at least 2 doses of vaccine, 91.2% were immune. The overall prevalence of anti–hepatitis A virus antibodies in unvaccinated children was 15.4%. In unvaccinated children >12 months of age, the rate of natural immunity was 11.7% (33 of 282). Interestingly, neither age nor ethnicity were associated with higher rates of natural infection. Among unvaccinated infants, the rate of passively maternal antibodies was surprisingly high (15 of 30 [50%]), mainly because of children from immigrant or Gypsy families, reflecting maternal natural infection. CONCLUSIONS: The implementation of universal vaccination against hepatitis A in Greece should be discussed because, according to our results, 11.7% of unvaccinated children have serologic evidence of past natural infection.