OBJECTIVES: In the United States (US), approximately 862 patients have haemophilia with inhibitors. Inpatient hospitalization is often required for treatment, which can lead to significant costs to hospitals, depending on the cause for hospitalization, and the associated length of stay and hospital resource use.  Variations in inpatient costs may also depend on patient inhibitor status to Factor VIII and the need for treatment with Factor VIII bypassing agents. A US hospital-based economic model was developed to estimate inpatient costs for on-demand treatment of bleeds of hemophilia patients with inhibitors and to quantify potential cost savings METHODS: An Excel-based model patterned the inpatient care associated with use of currently available bypassing agents: activated prothrombin complex concentrate (pd-aPCC) and recombinant Factor VIIa (rFVIIa) utilizing treatment-specific resource use, service and pharmacy costs, and source admission estimates based on a retrospective analysis of the Premier Perspective™ Database (1,218 inpatient stays with an ICD-9 diagnosis of hemophilia A identified from 2003-2008).  RESULTS: Within the Premier analysis, from 2003-2008 there were 4,560 male inpatient discharges (unweighted) with a Hemophilia A diagnosis. Of these, 252 showed use of a bypassing agent after excluding patients with OR charges and patients with inpatient stays with charges for both rFVIIa and pd-aPCC.  The final weighted sample sizes was 1,218 inpatient stays. In the base-case analysis, average per-patient costs associated with the inpatient treatment of hemophilia with inhibitors were slightly lower with rFVIIa as compared with pd-aPCC ($78,086 vs. $78,141).  CONCLUSIONS: Fast bleed resolution may confer significant inpatient cost savings through reductions in length of stay and duration of bypass agent treatment. Thus, rFVIIa can reduce overall treatment costs and reduce indirect costs since fewer resources are required, which reduces the economic burden of haemophilia on society. More comparative studies of these agents for on-demand treatment in the inpatient setting are still needed.