In North America, atrial fibrillation is associated with at least 75 000 ischemic strokes each year. Most of these strokes occur in patients older than 75 years of age. The high incidence of stroke in very elderly persons reflects the increasing prevalence of atrial fibrillation that occurs with advanced age, the high incidence of stroke in elderly patients, and the failure of physicians to prescribe antithrombotic therapy in most of these patients. This failure is related to the increased risk for major hemorrhage with advanced age, obfuscating the decision to institute stroke prophylaxis with antithrombotic therapy. This case-based review describes the risk and benefits of prescribing antithrombotic therapy for a hypothetical 80-year-old man who has atrial fibrillation and hypertension, and it offers practical advice on managing warfarin therapy. After concluding that the benefits of warfarin outweigh its risks in this patient, we describe how to initiate warfarin therapy cautiously and how to monitor and dose the drug. We then review five recent randomized, controlled trials that document the increased risk for stroke when an international normalized ratio (INR) of less than 2.0 is targeted among patients with atrial fibrillation. Next, we make the case that cardioversion is not needed for this asymptomatic patient with chronic atrial fibrillation. Instead, we choose to leave the patient in atrial fibrillation and to control his ventricular rate with atenolol. Later, when the INR increases to 4.9, we advocate withholding one dose of warfarin and repeating the INR test. Finally, when the patient develops dental pain, we review the analgesic agents that are safe to take with warfarin and explain why warfarin therapy does not have to be interrupted during a subsequent dental extraction.