The authors examined warfarin use in elderly patients with atrial fibrillation. Medical records were abstracted from a random sample of Medicare beneficiaries with atrial fibrillation who were discharged from Kansas hospitals. Data were analyzed for warfarin and aspirin use and risk factors for stroke or bleeding in patients 65-79 years of age or 80 years and older. Stroke risk factors other than age and atrial fibrillation were seen in 98% of 142 patients less than 80 years of age and 100% of 141 octogenarians. Warfarin use was similar in the younger and older age groups (50% vs. 45%, respectively; p = ns) and was not associated with the number of stroke or bleeding risk factors. Compared to patients less than 80 years of age, octogenarians were less likely to receive aspirin (38% vs. 27%, respectively; p < 0.05). Anticoagulation rates for high-risk patients with atrial fibrillation were low and poorly explained by stroke or bleeding risks.