Aim. To investigate the impact of hyperglycemia on the results of percutaneous coronary interventions (PCIs) in patients with acute ST-segment elevation myocardial infarction (ASTEMI). Subjects and methods. A study group consisted of 511 patients with hyperglycemia (blood glucose level (BGL) ≥7.77 mmol/L) who underwent primary PCIs in the period from 2005 to 2015. A comparison group included 579 patients (BGL ≥7.77 mmol/L). Results. Assessment of the results of hospital interventions revealed that the mortality rates in patients with hyperglycemia proved to be higher than in those with normal BGL (6.5 and 2.6%, respectively; p=0.002). No differences were found in the rates of stent thrombosis (1 and 1.4%; p=0.541) and recurrent myocardial infarction (1.2 and 1.6%; p=0.591). Major adverse cardiac events, including death, recurrent infarction, and stent thrombosis, were more frequently determined in the hyperglycemic patients (7.6 and 4.3%; p=0.020). No-reflow phenomenon statistically significantly more frequently developed in the patients with hyperglycemia (6.8 and 3.3%; p=0.007). Binary logistic regression analysis showed that the presence of hyperglycemia served as an independent predictor of hospital mortality (odds ratio (OR) 2.6; 95% confidence interval (CI), 1.4 to 4.8; p=0.002). The application of a random probability sampling technique revealed that mortality remained statistically significantly higher in the hyperglycemic patients than in the normoglycemic individuals at admission (6.7 and 2.6%; р=0.011). Conclusion. PCIs in patients with ASTEMI and hyperglycemia are characterized by higher mortality rates and the risk of major adverse cardiac events. Admission hyperglycemia is an independent predictor of hospital mortality.