The HLA allele HLA-B*27:05 on chromosome 6 is associated with antithyroid drug-induced agranulocytosis in white European individuals, according to a new genome-wide association study (GWAS). Three single nucleotide polymorphisms (SNPs; rs652888, rs199564443 and rs1071816) associated with this potentially life-threatening adverse effect of treating hyperthyroidism were also identified, one of which (rs1071816) was in moderate linkage disequilibrium with HLA-B*27:05. The findings, which complement two earlier GWAS in Asian populations, are a step towards precision medicine for antithyroid drug-induced agranulocytosis, which could see carriers of HLA-B*27:05 or the three SNPs being offered alternative treatments for hyperthyroidism.