Data related to the incidence and clinical outcome of acute myocardial infarction (AMI) in patients with preexisting coronary artery ectasia (CAE) are limited. We assessed whether infarct-related artery ectasia (EIRA) indicates an untoward clinical outcome in patients with AMI undergoing primary percutaneous coronary intervention (pPCI). Consecutive patients (n = 643) who presented with AMI and were treated with pPCI were analyzed retrospectively; 3 I patients (4.8%) had EIRA. Patients who had EIRA were significantly younger and had higher incidence of hypertension, previous stroke, smoking, inferior wall AMI, and Killip score >1. Infarct-related artery ectasia was more frequent in the right coronary artery (RCA). Impaired epicardial arterial flow, thrombus burden score of infarct-related artery (IRA), impaired Thrombolysis in Myocardial Infarction (TIMI) Myocardial Perfusion Grade, and distal embolization were significantly higher whereas ST-segment resolution and collateral vascular development were significantly lower in patients with EIRA. Infarct-related artery ectasia was an independent predictor of adverse outcome (odds ratio: 0.197; 95% confidence interval [CI]: 0.062-0.633; P = .006).