The development of thiopurine-induced pancreatitis in patients with IBD has been linked to the HLA-DQA1*02:01–HLA-DRB1*07:01 haplotype (rs2647087). The association was identified by genome-wide analysis of 172 patients and was validated in a separate cohort (n = 78). Patients with IBD who are heterozygous or homozygous at rs2647087 have a 9% and 17% risk of pancreatitis after thiopurine treatment, respectively.