OBJECTIVES: Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN), caused by allopurinol therapy, are strongly associated with the human leukocyte antigen (HLA), HLA-B*5801. It was unclear at what price the genetic testing would be a cost-effective strategy compared to no testing. This study aims to determine the range of genotyping cost that would be cost-effective from health care provider perspective. METHODS: A decision analytic model was used to estimate the cost-effectiveness of HLA-B*5801 genotyping compared to no testing. The incidence of SJS/TEN was estimated based on case reports from Health Product Vigilance Center of Thailand in year 2009. The prevalence of HLA-B*5801 was obtained from Thai population reported in dbMHC database, while the association of gene and SJS/TEN was based on a meta-analysis. Cost of SJS/TEN management and case-fatality rate were derived from National Inpatient Governmental Hospital Database in year 2007. We used PG5801 DNA detection kit as a genotyping tool with 100% sensitivity and specificity. We varied genotyping costs and selected values that would make the cost-effectiveness values being 100,000 or 300,000 THB/life year gained. One-way sensitivity analysis was undertaken to identify influential parameters. RESULTS: The estimated life years (LY) were 21.9999 and 21.9964 for testing and no testing groups, respectively. Setting the genotyping cost as 393 and 1,085 THB resulted in a potentially cost-effectiveness range of 100,000 and 300,000 THB/LY, respectively. The most influential parameters were the cost of genotyping and SJS/TEN management. CONCLUSIONS: : Pharmacogenetic testing for HLA-B*5801 appears to be potentially cost-effective if the testing cost falls in the range of 393 and 1,085 THB. It was important to note that this analysis has not taken into account sequelaes associated with SJS/TEN and has not performed based on  the societal perspective yet. Policy makers should consider our findings for guiding health policy during decision making process.