- Abstract Seropositivity against hepatitis A was examined among 4806 standing army personnel (4497 males and 309 females) during 1998–1999. Each bi-annual birth cohort examined showed a decline in seropositivity compared to the previous one. When compared with a study performed in 1989, however, for each of the 1961–1962, 1963–1964, 1965–1966, 1967–1968 and 1969–1970 birth cohorts examined, the 1998–1999 study showed 5–15% higher seropositivity. This trend remained after controlling for differences between the two studies in ethnic origin, sibship size and level of education. The overall seroconversion rate is estimated as 1.15% per year and the clinical to subclinical ratio as 1: 14. Thus, hepatitis A infection continues to occur in the young adult age group and vaccination of this group should be considered.