As many as one in four patients over age 40 will develop atrial fibrillation (AF), a significant risk factor for stroke. Although most clinicians are aware of the benefits of antithrombotic therapy, especially warfarin, for prevention of stroke, current guidelines for selection of antithrombotic therapy are confusing and inconsistently applied. The CHADS2 risk-stratification scheme, based on a clinical history of heart failure, hypertension, age >75, diabetes, or prior stroke, is a useful clinical tool to identify patients likely to benefit from warfarin, distinguishing these patients from patients at lower risk for whom aspirin is sufficient. Risk factors for intracerebral hemorrhage include anticoagulation intensity, hypertension, age, and previous stroke or cerebrovascular disease. Cerebral amyloid angiopathy and leukoaraiosis identified by high-resolution brain imaging are under investigation, but better schemes for stratifying bleeding risk are needed. In the future, new anticoagulants that are safer and easier to administer than warfarin will improve the benefit/risk burden for elderly patients with AF.