Background Intravascular ultrasound has become the standard invasive method for diagnosing coronary artery disease. The aim of the present study was to evaluate the ability of intravascular ultrasound for assessment of culprit lesion morphology during primary percutaneous coronary intervention (PCI) in patients with acute myocardial infarction (AMI).Methods We performed 18 intravascular ultrasound assessments preintervention during the primary PCI for AMI. intravascular ultrasound analysis included qualitative and quantitative measurements of reference and lesion extemal elastic membrane (EEM), lumen, and plaque plus media (P&M) area. Positive remodeling was defined as lesion/mean reference EEM >1.0. Culprit lesions were identified by a combination of electrocardiogram (ECG) and coronary angiography.Results There was an average of 1.44 infarct-related artery (IRA) plaques per patient. The incidences of thrombus and plaque ruptures were 28% (5) and 33% (6), respectively. Hypoechoic plaque was observed in 72% (13) of AMI patients. Calcified lesions could be found in 33% (6) of culprit lesions. Sixty percent of the culprit lesion sites presented with positive remodeling.Conclusions Intravascular ultrasound is a safe and feasible imaging modality in patients with AMI and can help identify plaque rupture, intracoronary thrombus or calcification. The culprit lesion site in AMI cases often presents with positive remodeling.