Alprolix (rFIXFc) is a recombinant extended half-life coagulation factor product. The purpose of this non-interventional study is to describe the real-world usage and effectiveness of Alprolix in the on-demand and prophylactic treatment of haemophilia B.

Inclusion Criteria:

• Have a diagnosis of haemophilia B and been treated previously with factor IX Product
• Have started Alprolix treatment prior to enrolment visit, or at enrolment prescribed treatment with Alprolix, regardless of participation in the study
• Signed and dated informed consent provided by the patient, or the patient's legally acceptable representative for patients under the legal age, before any study-related activities are undertaken. Assent should be obtained from paediatric patients according to local regulations

Exclusion Criteria:

• Participation in an investigational medicinal product trial at enrolment visit

All eligible patients who present for a routine Clinical visit will be asked to participate in the study by the treating physician at participating haemophilia treatment centres in France.