Background/Aims: Recently, the incidence of acute hepatitis A was reported to be increased. The purpose of this study was to characterize the patterns of acute hepatitis A and its relationship with anti-hepatitis A virus (HAV) seroprevalence in Kyungin province. Methods: We reviewed the medical records of 87 patients with acute hepatitis A who were diagnosed from October 1996 to August 1998 in Inha University Hospital. Then, the presence of IgG anti-HAV was evaluated for 2,401 persons who visited to our health promotion center. Results: Among the 87 patients, 79 patients (90.8%) were diagnosed in 1998. Thirty-seven patients (42.5%) were infected in their third decade and 28 (32.2%) were infected in their second decade. Totally, 71 patients (81.6%) were under the age of 31. Anti-HAV seroprevalence of persons who visited to health promotion center was 95.4%. The anti-HAV seroprevalence was significantly lower in the patients group aged under 31 than in the patients group aged over 30. Conclusions: The incidence of acute hepatitis A in Kyungin province is abruptly increased since 1998 and most of the patients were under the age of 31. It can be explained by a low anti-HAV seroprevalence of the population aged under 31. (Kor J Gastroenterol 1999;34:69 - 75)