Probabilistic sensitivity analysis results showing acceptability curves for the 3 treatment strategies over an 18-years-old until death time horizon for patients treated by using standard half-life FIX. Acceptability curves plot the probability that a given therapy is the “optimal” choice (y-axis), at a given willingness-to-pay threshold (x-axis). At a willingness-to-pay threshold of $50 000, on-demand treatment, prophylaxis, and gene therapy were cost-effective at respective probabilities of 57%, 0%, and 43%. At a willingness-to-pay threshold of $100 000, on-demand treatment, prophylaxis, and gene therapy were cost-effective at respective probabilities of 21%, 4%, and 75%. At a willingness-to-pay threshold of $150 000, on-demand treatment, prophylaxis, and gene therapy were cost-effective at respective probabilities of 4%, 4%, and 92%. On-demand and gene therapy treatment curves intersect at a willingness-to-pay threshold of $60 000/QALY, indicating that gene therapy is cost-effective in >50% of the simulations compared with on-demand treatment if a willingness-to-pay threshold of $60 000/QALY or more is considered. Similarly, prophylaxis and on-demand treatment curves intersect at a willingness-to-pay threshold of $156 000/QALY, indicating that prophylaxis is cost-effective in >50% of the simulations compared with on-demand treatment if a willingness-to-pay threshold of $156 000/QALY is considered.