Background: The AVERROES trial name is the following: The Apixaban Versus Acetylsalicylic Acid (ASA) to Prevent Stroke in Atrial Fibrillation Patients Who Have Failed or Are Unsuitable for Vitamin K Antagonist Treatment (AVERROES) trial demonstrated that apixaban reduced the risk of stroke relative to aspirin, without significantly increasing major bleeding risk in patients with atrial fibrillation (AF) considered unsuitable for warfarin therapy. Based on AVERROES trial results, this study compared the medical costs for clinical end points among patients with AF treated with either apixaban or aspirin.; Methods: Medical costs per patient-year for clinical events were determined. Based on clinical event rates for patients in the AVERROES trial, medical costs excluding drug costs were estimated for apixaban- and aspirin-treated patient groups.; Results and Conclusions: Based on AVERROES trial results, among patients with AF unsuitable for warfarin therapy, apixaban use was estimated to be associated with a mean medical cost avoidance of US$735 in a patient-year relative to aspirin. The primary driver was the significant reduction in ischemic stroke rate. The medical cost reduction associated with apixaban use was consistent in sensitivity analyses.