Hepatitis A is a disease with worldwide distribution. Conditions of sanitation and hygiene determine the overall epidemiological situation in any area, but risk behaviour determines an individual's chance of exposure. The recent licensing of formalin-inactivated vaccines for the prevention of hepatitis A requires an understanding of the epidemiology in order to devise how best to use this the vaccine in individuals or populations. Although higher-risk groups can be identified in developed countries, and vaccine will be useful to those groups, it is not likely that the vaccine will have a large effect on the prevalence of hepatitis A until it becomes a part of the routine childhood immunization schedule.