Nonvalvular atrial fibrillation (NVAF) is the most common sustained cardiac arrhythmia in clinical practice, which if untreated results in a doubling of cardiovascular morbidity and mortality. AF is an independent predictor of stroke, with an annual risk 5 to 6 times higher than patients in sinus rhythm.1 During recent years, several randomised clinical trials conducted by investigators around the world involving 13 843 participants with NVAF have demonstrated convincingly the value of warfarin therapies for stroke prevention in high risk patients.2-8 However, the dose response of warfarin is complex and its activity is easily altered by concurrent medications, food interactions, alcohol and illnesses. Adherence to medical advice and routine monitoring of the intational normalized ratio (INR) is important, because low anticoagulant intensity predisposes the patients to thromboembolic complications and high intensity to haemorrhage. Studies suggested that anticoagulant clinics could improve the quality of anticoagulation control,9 and anticoagulant clinics are common in west countries. However, in China, most AF patients taking warfarin usually attend the outpatient clinic of cardiology, while the quality of anticoagulation control is never investigated. We therefore assessed anticoagulation control in the outpatient clinic of cardiology, and the quality of anticoagulation control since the establishment of anticoagulant clinics.