OBJECTIVES: To measure the comparative direct medical care costs between incident warfarin patients who did or did not experience genotyping to guide dosing. METHODS: We reanalyzed the previously published MM-WES in which we demonstrated that genotyping reduces the risk of hospitalization for bleeding and thromboembolism in patients who initiate warfarin treatment in typical outpatient practice settings.  We used a cost consequence analysis to estimate the 6-month costs and consequences of warfarin genotyping.  The intervention group (IG) comprised 896 patients   and a comparison group was constructed from 2688 historical controls (HC).  The direct medical care costs were estimated for inpatient,  office visits and laboratory utilization (including cost of genotyping) and summed to a total cost per patient.  A boot-strapping method was performed to estimate confidence limits around the difference in mean cost per patient to assess statistical significance. RESULTS: Over the 6-month monitoring period, the all cause–related per patient costs for the genotyped IG patient was $4127 compared to $5040 for HC.  The all-cause difference of -$913 per patient reached statistical significance, 95% CI (-$895, -$930).  Various subgroup analyses including warfarin-related costs will be presented. CONCLUSIONS: Our analysis suggests that providing results of warfarin genotyping to treating physicians in typical outpatient settings produces cost-savings within six months of initiating warfarin therapy.  These estimates are likely conservative as they do not include ancillary costs such as rehabilitation or indirect costs, nor do they estimate costs beyond six months.