Abstract Objective — to analyze risk factors of stent thrombosis (ST) in patients with acute coronary syndrome (ACS) after percutaneous coronary intervention (PCI) and administration of dual anti-platelet therapy (DATT). Material and methods. There were 25 (1.1%) out of the 2378 patients with confirmed ST who underwent PCI with stenting for ACS in 2016—2018. These patients were included into the main group. The control group consisted of 158 patients without ST according to 12-month follow-up. Clinical, laboratory, instrumental, angiographic data and adherence to therapy were analyzed. Statistical analysis was performed using Statistica version 10.0 and MedCalc Software version 11.5.0. Results. The following significant risk factors of ST associated with patient’s condition were identified: severe acute heart failure (AHF) (Killip grade III—IV) (p<0.0001), ST elevation ACS (p=0.006), reduced left ventricular ejection fraction (p<0.0001), insulin-dependent diabetes mellitus type 2 (p=0.008), in-hospital paroxysmal tachyarrhythmias complicating the course of ACS (atrial fibrillation (p=0.001) and ventricular fibrillation (p=0.003). The most significant risk factors associated with coronary lesion and technical features of the procedure were acute occlusion of infarct-related artery (p=0.002), parietal thrombus (grade 1—5) before the primary PCI (p=0.0005), coronary artery dissection (p=0.0001), no-reflow phenomenon (p=0.02). There was a significant correlation between ST and low adherence to DATT (Moriscos—Green score 3 or less) (τ =0.61; p<0.0001). Conclusion. There is a multifactorial effect on the development of ST including patient-associated factors, features of coronary lesion and interventional techniques.