The clinical relevance of coronary artery ectasia (CAE) is poorly understood. We investigated the prevalence, potential predictors, and prognostic significance of CAE in patients with atherosclerotic coronary artery disease. Consecutive patients undergoing percutaneous coronary intervention (PCI) from January 2016 to December 2018 were included and followed up for 1 year. CAE was diagnosed as an abnormal dilation >1.5-fold the diameter of adjacent normal segments on angiography. A total of 590 patients with CAE were identified from 36 790 patients undergoing PCI (overall rate of CAE: 1.6%). In multivariate analysis, variables including body mass index >30 kg/m2 (risk ratio, RR: 2.413, P = .018), ever-smoking (RR: 1.669, P < .001), hypertension (RR: 1.221, P = .025), acute myocardial infarction at admission (RR: 1.343, P = .004), no diabetes (RR: .810, P = .023), previous myocardial infarction (RR: 1.545, P < .001), no left main disease (RR: .632, P = .008) and multiple-vessel disease (RR: 1.326, P = .001), increased C-reactive protein (RR: 1.006, P = .012) were predictors of CAE. The incidence of adverse cardiovascular outcomes did not differ significantly between patients with or without CAE ( P = .203). CAE is not uncommon among patients undergoing PCI in this cohort study. The presence of CAE vs its absence had no significant impact on 1-year clinical outcomes after PCI.