Although hepatitis A vaccination is recommended for persons with chronic liver disease, the cost-effectiveness of vaccinating patients with chronic hepatitis C virus has not been extensively studied. We evaluated its costs and benefits. A Markov model was used to assess cost-effectiveness from the health system and societal perspectives. Costs of hepatitis A screening and vaccination were compared with savings from reduced hepatitis A treatment and work loss to determine net costs of a "screen and vaccinate" strategy. Net costs were compared with longevity gains to assess cost-effectiveness. Based on hypothetical cohorts of 100,000 patients, vaccination would reduce the number of hepatitis A cases 63-72%, depending on patient age. Screening and vaccination costs of $5.2 million would be partially offset by $1.5-$2.8 million reductions in hepatitis A treatment costs and $0.2-$1.0 million reductions in work loss costs. From the health system perspective, vaccination would cost $22,256, $50,391, and $102,064 per life-year saved for patients vaccinated at ages 30, 45, and 60 yr, respectively. Cost-effectiveness ratios improve when work loss prevention is considered. Results are most sensitive to hepatitis A infection and hospitalization rates, and the rate used to discount future benefits to their present values. Hepatitis A vaccination of chronic hepatitis C patients would substantially reduce morbidity and mortality in all age groups examined. Consistent with other medical interventions for chronic hepatitis C patients, cost-effectiveness is most favorable for younger patients.