Acute necrotizing encephalopathy (ANE) is a rare and severe syndrome of acute encephalopathy triggered by viral infections. Cytokine storm is considered as the main pathogenetic mechanism of ANE. ANE is prevalent in East Asia, suggesting the association of host genetic factors. To elucidate the genetic background of Japanese ANE, we examined genotypes of human leukocyte antigen (HLA)-A, C, B, DRB1, DQB1 and DPB1 in 31 patients. Significant positive association was observed in both the allele frequency and positivity of DRB1*09:01 (P=0.043 and 0.025, respectively), as well as those of DQB1*03:03 (P=0.034 and 0.026, respectively). The carrier frequency of DRB1*09:01 and DQB1*03:03 alleles was higher in the patients (45.16%) than in controls (28.57%). These alleles are more common in East Asian than in European populations, and are reportedly associated with various autoimmune diseases in Japanese patients. Our data provide further evidence that altered immune response based on individual HLA genotypes may contribute to ANE pathogenesis.