Atrial fibrillation significantly raises the risk for ischemic stroke, and the prevalence of atrial fibrillation is increasing due to the aging of the population. Reducing the risk of ischemic stroke is one of the cornerstones in the medical management of atrial fibrillation. Oral vitamin K antagonists such as warfarin are highly effective in preventing atrial fibrillation-related thromboembolism, but can be challenging to manage and are associated with increased bleeding risk. Aspirin therapy has modest efficacy in reducing stroke risk, but is much less effective than warfarin. To help guide the choice of optimal antithrombotic therapy, risk stratification for stroke in atrial fibrillation may be helpful, although most elderly patients derive a net benefit from warfarin. Older patients have higher bleeding rates on warfarin and are at higher risk for intracranial hemorrhage. Although the risk of intracranial hemorrhage is generally quite low, its occurrence is associated with significant mortality and disability, and more effective methods to risk stratify patients for intracranial hemorrhage are needed.