Improving the management and prevention of stroke is a priority for the NHS. Atrial fibrillation (AF) is widely recognised to be a major cause of stroke. Moreover, it is a preventable cause in that the increased risk of stroke associated with AF can be markedly reduced by anticoagulation with warfarin. Yet a substantial number of cases of AF remain undetected and untreated. Of more concern, even after identification of AF, many individuals at high risk of stroke do not receive warfarin. This article reviews the evidence on the importance of AF as a cause of stroke and assesses the benefits of anticoagulation and our reluctance to anticoagulate. Finally, it explores ways of improving on current practice, to increase the proportion of patients with AF receiving anticoagulants.