Objective: To determine the frequency of acute stent thrombosis after primary percutaneous coronary intervention in patients with ST-elevation myocardial infarction. Study Design: Descriptive cross sectional study. Place and Duration of Study: Department of Cardiology, National Institute of Cardiovascular Disease Hospital, Karachi from 30th 2017 to 31st December 2017. Methodology: One hundred and sixty three patients will undergo primary percutaneous coronary intervention and stent either drug-eluting stents (coated with medication) or bare-metal stent was placed. Patients who developed sudden onset of typical chest pain, indicating acute ischemia in the distribution of the target vessel (in which stent was placed), in these patient’s angiography was done (relooked) if it showed complete occlusion within the stented segment with evidence of thrombus, patient was labeled as having acute stent thrombosis. Results: There were 117 (71.7%) males and 46 (28.23%) were females with mean age of 51.78±13.09 years. Drug-eluting stents was placed in 87(53.37%) and bare metal was placed in 76(46.63%) patients. Positive acute stent thrombosis was 2 (1.23%). Conclusion: The frequency of acute stent thrombosis after primary PCI was found to be 1.23%. Keywords: ST-elevation myocardial infarction (STEMI), Percutaneous coronary intervention (PCI), Acute myocardial infarction, Stent thrombosis