In this genetic association study of 16 patients with adjudicated allopurinol-induced Stevens-Johnson syndrome and toxic epidermal necrolysis or drug reaction with eosinophilia and systemic symptoms from a heterogenous US-based population, an association with the established risk allele HLA-B*58:01 was demonstrated, and HLA-A*34:02 was identified as an additional independent risk factor. This evidence concerns the gene HLA-A and Increased total eosinophil count.