BACKGROUND: Atrial fibrillation is the most common cardiac arrhythmia associated with significant medical complications. We examined trends in the medical therapy of atrial fibrillation in the United States from 1991 through 2000. METHODS: Data from 1355 visits among patients with atrial fibrillation were obtained from the National Ambulatory Medical Care Survey, a nationally representative assessment of office-based practice. We assessed trends in medication use for ventricular rate control (digoxin, beta-blockers, and calcium channel blockers), sinus rhythm maintenance (class IA, IC, and III antiarrhythmics), and thromboembolism prevention (oral anticoagulants and aspirin). RESULTS: Overall rate control medication use decreased from 72% of visits in 1991-1992 to 56% in 1999-2000 (P =.01 for trend) due to declining digoxin use (64% to 37%, P.001 for trend). beta-Blocker and calcium channel blocker use remained unchanged. Although there was no change in overall sinus rhythm medication use over time, amiodarone hydrochloride use increased from 0.2% to 6.4% (P.001 for trend), while quinidine use decreased from 5.0% to 0.0% (P =.01 for trend). Oral anticoagulant use increased (28% to 41%, P =.01 for trend), with the greatest increase in patients aged 80 years and older (14% to 48%, P.001 for trend). Despite this, only 46.5% of patients at high risk for stroke were taking anticoagulants in 1999-2000. CONCLUSIONS: Digoxin use in atrial fibrillation decreased over time, without concomitant increases in beta-blocker or calcium channel blocker use. Miodarone replaced quinidine as the dominant sinus rhythm medication. Although oral anticoagulant use increased over time, particularly in the oldest patients, fewer than half of the patients at high risk for stroke were anticoagulated.