BackgroundAutoimmune disease is one of the leading causes of morbidity and mortality worldwide. In Addisons disease, the adrenal glands are targeted by destructive autoimmunity. Despite being the most common cause of primary adrenal failure, little is known about its aetiology. MethodsTo understand the genetic background of Addisons disease, we utilized the extensively characterized patients of the Swedish Addison Registry. We developed an extended exome capture array comprising a selected set of 1853 genes and their potential regulatory elements, for the purpose of sequencing 479 patients with Addisons disease and 1394 controls. ResultsWe identified BACH2 (rs62408233-A, OR = 2.01 (1.71-2.37), P = 1.66 x 10(-15), MAF 0.46/0.29 in cases/controls) as a novel gene associated with Addisons disease development. We also confirmed the previously known associations with the HLA complex. ConclusionWhilst BACH2 has been previously reported to associate with organ-specific autoimmune diseases co-inherited with Addisons disease, we have identified BACH2 as a major risk locus in Addisons disease, independent of concomitant autoimmune diseases. Our results may enable future research towards preventive disease treatment. Funding Agencies|Swedish Research Council; Torsten Foundation; Ragnar Soderberg Foundation; European Union [201167]; Stockholm County Council; Karolinska Institutet; Swedish Society for Medical Research; Swedish Society of Medicine; NovoNordisk Foundation; Tore Nilsons Foundation for Medical Research; Swedish Research Council Formas; Knut and Alice Wallenberg Foundation; Marianne and Marcus Wallenberg Foundation; Swedish Reumatism Foundation; King Gustaf Vs 80-year Foundation; Ake Wiberg Foundation; AstraZeneca Science for Life Laboratory Research Collaboration grant (DIS-SECT)