Hepatitis A infection is caused by the hepatitis A virus (HAV), which is transmitted through the fecal-oral route. Lifelong protective antibodies are present after infection. The number of cases of adult hepatitis A has progressively been increasing during the last several decades in Korea. In addition, the pattern of age-specific seroprevalence of anti-HAV has changed with economic growth. The prevalence of anti-HAV in the 10-50-year age range has declined rapidly during the last 3 decades. As a result, this age group has a high risk for HAV infection and clinically overt hepatitis A is increasing in adolescents and adults. It is well established that the severity of the disease is related to the age of the patients. The development of more cases of adult hepatitis A with severe presentation is expected in the near future. The clinical features and the epidemiological shift of HAV underscore the importance in Korea, as well as in other countries with similar issues, of childhood vaccination and consideration of catch-up vaccination for adolescents and adults as well as of targeted vaccination for individuals at increased risk for infection or its complications. There is a need to extensively evaluate the nationwide epidemiology of HAV infection, make cost-benefit analyses of HAV vaccination, and establish guidelines for HAV vaccination.