The aim of the present paper was to study the implementation of new medical knowledge. We investigated whether Danish doctors have implemented new national guidelines for oral anticoagulation of atrial fibrillation. An anonymous questionnaire with six standardized case stories was sent to 315 general practitioners in the county of Viborg and Ringkøbing, 79 heads of departments of medicine and cardiology, and 20 heads of departments of neuromedicine across the country. The answers showed that the Danish doctors recommended anticoagulant therapy only to a low extent for this group of patients despite the guidelines and the scientific evidence. The reasons for not choosing anticoagulant therapy were lack of knowledge concerning risk of stroke associated with the disease, worries about the disadvantages of the treatment, and lack of knowledge of its benefits. It is concluded that despite solid scientific documentation and an intensive implementation process of guidelines, issued by well-known respected colleagues in a small homogeneous country as Denmark (5 million inhabitants), knowledge of new research findings varies greatly and is generally limited. To obtain optimal use of new research findings, a powerful implementation effort must be recommended and the study reveals a need for a closer link between research and post-graduate education.