Background: Multivessel coronary artery disease is a common finding during the primary percutaneous coronary intervention in patients with acute ST‑segment elevation myocardial infarction (STEMI). It might be a cause for recurrent attacks. This study aimed to evaluate nonculprit lesions (NCLs) encountered in the three major epicardial coronary arteries. Methods: Patients with STEMI who underwent PPCI and matched the study inclusion criteria were enrolled. They were evaluated clinically, biomedically, and coronary angiographically. The coronary angiography analysis was examined by four cardiologists using the Quantitative Coronary Artery Analysis software. The data was analyzed statistically. Results: Of the 154 patients included in the study, 130 (84.4%) were males and 24 (15.6%) were females, with a mean age of 52.92 ± 13.14 years. Five hundred seventy‑four NCLs were found in 132 (85.7%) patients. Nonobstructive lesions with stenosis less than 70% of vessel diameter were more frequent than obstructive lesions. The left circumflex coronary artery (LCX) was the first one of the three major arteries to be affected by obstructive NCLs. The obstructive NCLs were 128 in number; found in 78 (50.4%) patients; 65 (50.8%) of them were in LCX; 32 (25%) were in left anterior descending (25%); and 31 (24.2%) were in right coronary artery. Conclusions: NCLs are common among STEMI patients. LCX obstructive NCLs are comparable to those in the other two major epicardial coronary arteries, with respect to frequency and severity of luminal stenosis.