OBJECTIVES: Hemophilia B is a rare condition and evidence of specific health and economic outcomes for it are relatively scarce. The purpose of this study was to assess economic and health consequences of prophylaxis vs on-demand supply of factor IX (FIX) in young patients diagnosed with moderate/severe hemophilia B, from the perspective of Instituto Mexicano del Seguro Social (IMSS). METHODS: A three-state, two-week cycle Markov model followed moderate/severe hemophilia B patients starting at age 2 until they reached 18 years. Patients in prophylaxis received 64.6 IU recombinant FIX/kg per infusion and 2.77 infusions every two weeks (same dose used in spontaneous bleeds), while patients in the on-demand arm received 69.4 IU plasma-derived FIX/kg to manage spontaneous bleeds. A literature review for outcomes in hemophilia B was performed (rates of bleeding with prophylaxis and on-demand therapy, average doses). Weight and probability of death per age correspond to the Mexican population. Avoided bleeds were the effectiveness measure used. The model does not consider other costs than FIX acquisition costs and emergency room, which were extracted from IMSS´s sources (except the cost of recombinant FIX, provided by the manufacturer). Costs are expressed in 2012 US$. Costs and consequences were discounted at 5%/annum. Univariate sensitivity analysis was performed. RESULTS: The prophylaxis group experienced 49% fewer bleeds than the on-demand group (39.11 vs. 83.32 per patient, respectively), however, this is reached with an incremental cost of $817,818.89 (cost of prophylaxis was $920,411.15, almost nine times the cost of on-demand). In spite of this, ICER for prophylaxis was $18,500.63/avoided bleed. The model is highly sensitive to probability of spontaneous bleeding, doses and cost of acquisition of FIX. CONCLUSIONS: At IMSS, prophylaxis with recombinant FIX for the management of patients with moderate/severe hemophilia B would be an intervention with strong health benefits worth the additional investment required.