Conflicting data is present in the literature about patients who are treated with percutaneous coronary intervention (PCI) due to the exaggeration of the non culprit artery. The precise understanding of the non culprit artery in the setting of ST segment elevated myocardial infarct (STEMI) is important since the time and modality of the treatment is planned accordingly. The aim of this study is to evaluate the lesions in the non culprit coronary artery during primary PCI and control coronary angiography (CAG) using quantitative coronary angiography (QCA) in multivessel STEMI patients. In this study, multivessel disease STEMI patients whom underwent primary PCI between January 2010 and March 2011 were included. Critical stenosis degree was accepted as ≥70 % in the non culprit artery. All patients were evaluated with control CAG 1 month after primary PCI. Assessment with CAG was performed by two blinded cardiologists. QCA program was used to evaluate reference artery diameter (RAD), minimum luminal diameter (MLD) and degree of stenosis. With regard to the degree of stenosis, significant reduction was accepted as ≥15 % while % 5–15 decrease was accepted as moderate. Of the 81 patients, 61 were males and 20 were females (mean age 58.1 ± 10). In the control CAG, the degree of non culprit artery stenosis was found to be decreased (p < 0.001) while RAD and MLD were increased (p < 0.001 and p < 0.001 respectively). Significant decrease in critical non culprit artery lesions was detected in 22 patients (20.9 %) meanwhile moderate reduction was observed in 26 patients (24.7 %). In 14 patients (13.3 %), non culprit artery lesions accepted as critical during primary PCI were found to be non critical during the control CAG. Planned intervention was cancelled and medical treatment was initiated in those 14 patients. Our data indicated using QCA, approximately the half of non culprit lesions were found less critical during control CAG when compared to primary PCI. Therefore, it is concluded that complete revascularization during primary PCI should be avoided in multivessel STEMI patients and critical non culprit artery lesions should be re-evaluated with later control CAG.