We constructed a decision model to simulate costs and benefits for persons in the context of hepatitis A prevention. Three strategies were compared: i) no intervention; ii) vaccination against hepatitis A without screening; iii) vaccination against hepatitis A for those susceptible after screening for anti-HAV.  We divided the population into 3 age groups: 3-11 years, from the King Chulalongkorn Memorial Hospital.  Relevant probabilities were obtained from published literature and expert opinion. At the present incidence of hepatitis A infection, in all age groups examined, the net benefits of a universal no-intervention strategy were higher than those of either vaccination (intervention) strategy. The cost of vaccination without screening in the 3-11-year and 12-18-year groups would equal the benefit if the incidence rates amounted to approximately 138 and 212 infected individuals per 100,000, respectively, that of vaccination with screening at incidence rates of about 200 and 260 infected persons per 100,000, respectively.  In the 19-40-year group, the cost incurred by vaccination either with or without screening would equal the benefit at an incidence rate above 450 infected individual per 100,000.  For the benefits to outweigh the estimated vaccination costs at present the vaccine is still too expensive.  The cost of vaccination without screening in the 3-11-year group would equal the benefit if the cost of vaccine was about 586 baht/2 doses (293 baht/dose), and about 500 baht/2doses (250 baht/dose) in the 12-18-year group. Likewise, because of the cost of vaccine, it would not be cost-beneficial in the 19-40-year group both with and without screening, and neither would it be in the 3-11-year and 12-18-year groups including screening. According to current standards, under the conditions of the present study the benefit of hepatitis A vaccination administrated to the general population between the age of 3 and 40 years in Thailand dose not justify the expenses incurred.  Major changes in hepatitis A incidence, anti-HAV seroprevalence, vaccine cost or the treatment outcome would be required to potentially render either intervention strategy cost beneficial.