Aim: To derive a new clinical score to improve the prediction of those at risk of poor International Normalized Ratio control among patients with atrial fibrillation taking vitamin K antagonists. Materials & methods: The score was calculated using PAULA database and validated in the FANTASIIA population. Results: The DAFNE score (cardiovascular Disease, concomitant treatment with Amiodarone, Food/dietary transgression and taking ≥7 pills daily, fEemale sex) score was related to a higher probability of poor International Normalized Ratio control. C-indexes were 0.611 and 0.576 (De Long test, p = 0.007) for the DAFNE and SAMe-TT₂R₂ scores, respectively. Conclusion: The DAFNE score is a new clinical score which may potentially help determine those patients with atrial fibrillation who are at high risk of poor anticoagulation control with vitamin K antagonists.