BACKGROUND Primary percutaneous coronary intervention (PCI) is the main treatment for patients with ST-segment elevation myocardial infarction (STEMI). We investigated factors affecting the major complications of this procedure. METHODS This case-control study assessed 200 patients receiving primary PCI for STEMI. Effects of some factors including age, sex, coronary artery risk factors, left ventricular function, thrombolysis in myocardial infarction (TIMI) flow, and number of involved vessels on major adverse cardiac events (MACE) were studied. RESULTS Two thirds of patients were male but sex had no significant effect on MACE. Similarly, age, hypertension, and hyperlipidemia did not significantly affect the incidence of MACE. However, Killip class, left ventricular ejection fraction, diabetes, TIMI flow, and type of involved vessels had significant relations with the incidence of MACE. CONCLUSION According to our findings, factors such as diabetes, left ventricular function, left anterior descending artery involvement, and low TIMI flow are risk factors of MACE.