In our recent study on genetic variants in the HNF1 gene in dead and living opioid addicts (1) we had obtained a permission to perform the study from the National Health Committee on Health Research Ethichs with the Project ID of 1406709. Due to a misunderstanding we wrote “Project ID 23555” in the letter. This is the Project ID for the mother study (2) on which the letter is based.We apologize for any inconvenience this may have caused. (1) Nguyen A, Stage TB, Feddersen S, Christoffersen DJ, Christensen MM, Damkier P, Thomsen JL, Brøsen K (2016) Carriers of genetic variants in the HNF1A gene are more common among dead opioid addicts than among living addicts. Eur J Clin Pharmacol 72:1159-1160. doi:10.1007/s00228-016-2076-3 (2) Christoffersen DJ, Damkier P, Feddersen S, Möller S, Thomsen JL, Brasch-Andersen C, Brøsen K (2016) The ABCB1, rs9282564, AG and TT genotypes and the COMT, rs4680, AA genotype are less frequent in deceased patients with opioid addiction than in living patients with opioid addiction. Basic Clin Pharmacol Toxicol 119(4):381-388. doi: 10.1111/bcpt.12602.