Etranacogene dezaparvovec (etranacogene dezaparvovec-drlb; Hemgenix ® ) is an adeno-associated virus vector-based gene therapy being developed by uniQure and CSL Behring for the treatment of haemophilia B. In November 2022, etranacogene dezaparvovec was approved in the USA for the treatment of haemophilia B [congenital factor IX (FIX) deficiency] in adults who are currently using FIX prophylaxis therapy, have current or historical life-threatening haemorrhage or have repeated, serious spontaneous bleeding episodes. In December 2022, etranacogene dezaparvovec also received positive opinion in the EU for the treatment of haemophilia B. This article summarizes the milestones in the development of etranacogene dezaparvovec leading to this first approval.