This study examined warfarin usage for elderly Medicare beneficiaries with atrial fibrillation (AF) who suffered traumatic brain injury (TBI), hip fracture, or torso injuries. Using the 5% Chronic Condition Data Warehouse administrative claims data, this study included fee-for-service Medicare beneficiaries who had a single injury hospitalization (TBI, hip fracture, or major torso injury) between 1/1/2007 and 12/31/2009, with complete Medicare Parts A, B (no Medicare Advantage), and D coverage 6 months before injury, and who were aged 66 years or older and diagnosed with AF at least 1 year before injury. About 45% of the AF patients were using warfarin before TBI or torso injury, and 35% before hip fracture. After injury, there was a dramatic and persistent decrease in warfarin use in TBI and torso injury groups (30% for TBI and 37% for torso injury at 12 months after injury). Warfarin usage in hip fracture patients also dropped after injury but returned to pre-injury level within 4 months. TBI and torso injury lead to significant decreases in warfarin usage in elderly AF patients. Further research is needed to understand reasons for the pattern and to develop evidence-based management strategies in the post-acute setting.