There is evidence that patients with atrial fibrillation (AF) are not being anticoagulated according to the published guidelines. Difficulty in identifying such patients may partly explain this. In this study, we examined the yield of different methods for detecting people with AF in a single general practice: hospital discharge letters, referrals to cardiology, staff recall of cases, records of relevant prescriptions from the local pharmacist and similar records from the GMS Payments Board. A review of all files of patients over 45 was undertaken as the definitive method of case identification. Recommended anticoagulation guidelines were applied using structured patient interviews. The practice population was 5,473. Sixty-eight patients with AF were identified giving a practice prevalence of 1.2%. The GMS Payment Board records for the prescribing of all specified medications was the most sensitive method (58.8%) with a positive predictive value of 21.6%. Of nine patients without cognitive impairment at consultation, four (44.4%) opted to change to the recommended treatment. Reluctance of patients to adopt current treatment guidelines points to the need for further work in this area.