Introduction: Multivessel disease in ST-elevation myocardial infarction (STEMI) is associated with a worse prognosis. A multivessel approach at the time of primary percutaneous coronary intervention (PC!) is the subject of debate. Objective: To assess the impact of a multivessel approach on in-hospital morbidity and mortality in patients with STEMI undergoing primary PCI. Methods: We studied patients from the Portuguese Registry of Acute Coronary Syndromes with STEMI and multivessel disease who underwent primary PCI. The 257 patients were divided into two groups: those who underwent PCI of the culprit artery only and those who underwent multivessel PCI. Cardiovascular risk factors, STEMI location, in-hospital treatment, number and type of diseased and treated arteries, type of stent implanted and ejection fraction were recorded. The primary end-point was defined as in-hospital mortality and the secondary end-point as the presence of at least one of the following complications: major bleeding, need for transfusion, invasive ventilation, heart failure and reinfarction. Results: Multivessel disease was found in 43.3% of the study population and a multivessel approach was adopted in 19.2% of these patients. There were no differences between the groups in cardiovascular risk factors or electrocardiographic presentation of STEMI. Patients undergoing multivessel PCI were more likely to be treated with drug-eluting stents and glycoprotein IIb/IIIa inhibitors, and less likely to receive heparin therapy. There were no differences between the groups with regard to in-hospital mortality or the incidence of complications. Conclusion: In our population of patients with STEMI, a multivessel approach appears to be safe and not associated with increased in-hospital mortality or morbidity. (C) 2012 Sociedade Portuguesa de Cardiologia. Published by Elsevier Espana, S.L. All rights reserved.