Aim: To assess the quality of real-life warfarin anticoagulation in patients requiring chronic thromboprophylaxis in a southern Croatian county. Methods: We retrospectively analyzed international normalized ratio (INR) values determined over one year (2016-2017) at the Zadar County General Hospital in warfarin-treated patients requiring chronic thromboprophylaxis. The values represent 83.0% of all INRs and were determined in 84.0% of all warfarin-treated patients in the county during the observed period. Results: Overall 31 162 INRs were taken from 3697 patients, 2240 of whom (20 851 INRs, 3-56 per patient, median 9) were referred with diagnoses requiring chronic thromboprophylaxis: mainly atrial fibrillation/flutter (n = 1508, 14 902 INRs) but also cardiac implants, valvular disease, severe heart failure, and cerebrovascular disease (“other”, n = 732, 5949 INRs). Only 50.1% of all INRs were within the target range, 2.0-3.5, while 43.6% were <2.0, and 6.3% were >3.5. Median crude individual proportion of INRs within the range was 50.0%, while it was 42.0% for INRs <2.0. Only 23.0% of the patients had ≥70% of the INRs within the target range (adequately anticoagulated), while 35.5% had ≤33.3% of the INRs within the range. Conversely, 66.5% of the patients had ≥33.3% INRs <2.0. Adjusted probability of adequate anticoagulation in atrial fibrillation/flutter patients was consistently 25.5% to 27.7%, regardless of the number of determined INRs, while in patients with other conditions it increased from 9.5% to 25.2% with a higher number of INRs. Conclusion: The achieved level of warfarin anticoagulation in this real-life setting is far below what is needed for effective long-term thromboprophylaxis.