Background: Pain is a common symptom of hemophilia that may adversely affect patients’ quality of life (QoL). Previous post hoc analyses of prophylaxis with recombinant factor IX Fc fusion protein (rFIXFc) have been published for adults and adolescents, demonstrating improvements in health-related QoL (HRQoL) when assessed by the haemophilia-specific QoL (HaemAQoL) questionnaire. Objective: To describe in depth the evolution of QoL, pain- and activity-related domains and questions for pediatric, adolescent, and adult patients with hemophilia B treated with rFIXFc prophylaxis. Design: A post hoc analysis of data from a series of clinical trials. Methods: This post hoc, long-term analysis assessed patient-reported outcomes (PROs) from the Kids B-LONG (NCT01440946: pediatric) and B-LONG (NCT01027364: adults and adolescents) parent studies and the B-YOND (NCT01425723: all age groups) extension study. Results: Ninety-two adult and adolescent patients that started in the B-LONG study were assessed, with a median (range) duration of follow-up of 58.9 (0.0–78.4) months. The Haem-A-QoL total score was significantly reduced from baseline by 4.45 (p ⩽ 0.01), as were the subdomains ‘physical health’ (9.10; p = 0.001), ‘sports and leisure’ (11.25; p ⩽ 0.01), ‘treatment’ (2.69; p = 0.05), and ‘view of self’ (5.81; p = 0.002). Thirty pediatric patients that started in the Kids B-LONG study were assessed, with a median (min–max) duration of follow-up of 36.7 (9.0–59.9) months. The high level of satisfaction demonstrated by the PROs at baseline was maintained. Conclusion: rFIXFc prophylaxis reduced perceived pain and increased levels of physical activity with sustained, long-term improvements in QoL in adult and adolescent patients with hemophilia B and maintained high QoL scores in pediatric patients. Plain language summary Helping to reduce pain and increase physical activity in patients with hemophilia B People with hemophilia B do not produce factor IX (FIX) that works properly, so they need to be given additional FIX to help their blood clot. Recombinant factor IX Fc fusion protein (rFIXFc), is an extended half-life (meaning it remains active for longer than standard, unmodified FIX) treatment for hemophilia B. People with hemophilia B can experience episodes of bleeding, which can result in other symptoms, including pain, difficulty participating in sport, and poor mental health. This study shows that regularly taking rFIXFc over approximately 5 years to prevent or treat bleeds could also help to make these other symptoms better.