The incidence of hepatitis A has declined in the United States for several decades, leading to an increased number of susceptible adolescents and adults. Because clinical severity increases with age, hepatitis A infections in older individuals cause greater morbidity, mortality, and treatment costs. Because the economic burden of hepatitis A has not been well described, we estimated its costs, from the societal perspective, for patients infected at distinct ages. A case-series study described treatment patterns, work loss, and symptom duration. Disease outcomes were estimated by an expert panel. Economic losses were calculated by applying normative data reflecting treatment charges, employee compensation, and the value of housekeeping services. In the case-series study, mean treatment charges were $740 for nonhospitalized patients versus $6,914 for hospitalized patients (P <.001). Symptom duration (67.8 vs. 34.4 days, P <.001) and work loss (33.2 vs. 15.5 days, P <.01) were also greater for those hospitalized. Nationally, we estimate 63,363 symptomatic hepatitis A infections occurred among adolescents and adults during 1997, resulting in 8,403 hospital admissions and 255 deaths. Nearly 2.5 million days of symptomatic illness and 829,000 work-loss days resulted, and 7,466 years of life were lost. Under base-case assumptions, annual hepatitis A costs were estimated at $488.8 million. In sensitivity analyses, this estimate varied from $332.4 to $579.9 million. These costs may be reduced by regionally targeted vaccination of children, as recommended by the Advisory Committee on Immunization Practices, although the cost effectiveness of this policy has not yet been established.