© 2021 Tehran University of Medical Sciences.Background: Atrial fibrillation (AF) is associated with increased morbidity in myocardial infarction (MI), especially thromboembolic risk increases. The PRECISE-DAPT (The PREdicting bleeding Complications In patients undergoing Stent implantation and subsEquent Dual Anti-Platelet Therapy) score was created to predict the bleeding risk of dual antiplatelet therapy. The purpose of this study was to evaluate the association between new-onset AF and the PRECISE-DAPT score in ST-segment-elevation myocardial infarction (STEMI). Methods: This retrospective study enrolled patients who developed STEMI within 12 hours of the onset of symptoms and underwent primary percutaneous coronary intervention. The study population was divided into 2 groups of PRECISE-DAPT scores of 25 or greater and PRECISE-DAPT scores of below 25 and their baseline characteristics, as well as laboratory and echocardiography results, were compared. In-hospital new AF and related events were compared between the 2 PRECISE-DAPT score groups. Results: From February 2015 to December 2017, this study enrolled 2234 patients with STEMI at a mean age of 54.4 years. The new-onset AF incidence rate was higher in the higher PRECISE-DAPT group than in the lower PRECISE-DAPT group (62 [28.7 %] vs 58 [2.9%]; P<0.001). According to the multivariate logistic regression analysis, the factors associated with new-onset AF were the left atrial diameter (OR=1.98, 95% confidence interval=1.34–2.93; P=0.001) and the PRECISE-DAPT score (OR=1.04, 95% confidence interval=1.10–1.18; P<0.001). Conclusion: The PRECISE-DAPT score was associated with the development of new-onset AF in our patients with STEMI. Further follow-up of these patients will provide clearer information.