Hepatitis A infection is a common disease in tropical countries, including Thailand. Hepatitis A vaccination of children and adolescents has been recommended by many countries.  We performed a cost-benefit analysis in order to determine the best strategy for Thailand. Three strategies were tested: a) no intervention; b)to set the path probability of each strategy.  The cost of intervention of each strategy was identified; the outcome cost was the total economic loss due to hepatitis A infection as the result of each strategy.  Benefit was the final total cost according to each strategy (cost of intervention and economic loss due to possible hepatitis A infection).  Surprisingly, the most benefit was gained from a strategy of no intervention. Vaccination after screening was the worst strategy. Our results indicated that hepatitis A vaccination for Thai adolescents was not cost-effective.