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Warfarin is widely used in patients with non-valvular atrial fibrillation (AF) because it is effective in reducing thromboembolic complications. However, it has a narrow safe therapeutic window. We aimed to examine the frequency of maintaining this therapeutic window in daily practice.We enrolled consecutive patients with non-valvular AF presenting to five busy general hospitals in Kuwait for regular international normalised ratio (INR) testing. Patients were required to be on warfarin for more than 3 months and to have had at least 5 INR measurements. We recorded up to 20 INR measurements per patient. Time in therapeutic range (TTR) was assessed by the Rosendaal method and the percentage of INR measurements in the therapeutic range was recorded.A total of 369 patients with non-valvular AF underwent 4392 INR measurements. (mean age 62.89 ± 11 years, 56% women, 78% had hypertension and 58% had diabetes). Mean duration of warfarin use was 13 ± 9.1 months. Of all INR measurements, 47% were in the therapeutic range of 2-3 and TTR by Rosendaal method was 52.6%.The quality of anticoagulation with warfarin in non-selected daily practice in Kuwait is poor. This could have serious implications for patients' outcomes.