OBJECTIVES: The management of atrial fibrillation (AF) represents a significant and increasing burden on the UK National Health Service (NHS).  Understanding this burden is important in informing healthcare planning and policy development. This study was conducted to describe the NHS costs associated with AF management in routine UK clinical practice.    METHODS: A retrospective observational study of 825 patients with AF was undertaken in 8 UK primary care practices in 2010.  Data were collected from the clinical records of all eligible, consenting patients, for a period of up to 3 years.  The first 12 weeks following diagnosis was defined as the ‘initiation phase’; the period after week 12 was defined as the ‘maintenance phase’. RESULTS: Mean (SD) total cost of AF management was £947/€1,153/1,476USD (£1,098/€1,337/$1,711) per patient in the initiation phase and £469/€571/$731 (£597/€727/$930) per patient year in the maintenance phase. Inpatient admissions and secondary care attendances accounted for 83% of total initiation phase and 64% of total maintenance phase costs.  Significant variables contributing to high cost in the initiation phase were co-morbid hypertension and lower patient age, although only accounting for 5% of cost variability. Significant variables in the maintenance phase (18% of cost variability) were co-morbid congestive or structural heart disease and diabetes, and day-care attendances, ECGs and hospitalisations in the initiation phase. Mean maintenance phase costs were higher for patients managed by practices providing anticoagulation services (£555/€676/$865) than patients receiving secondary care anticoagulation (£421/€513/$656, p=0.002). CONCLUSIONS: The study confirms that inpatient admissions and secondary care attendances contribute most to total AF management costs. None of the variables analysed accounted for much variability in the total cost of AF management, suggesting that it is often not possible to predict which patients will be high NHS resource users. Future work should focus on how to safely reduce avoidable hospital admissions.