Background: For patients with STEMI without cardiogenic shock who are undergoing primary PCI, current guidelines do not recommend intervention on non-culprit vessels. However, limited data are available on cardiogenic shock. We investigated the clinical impact of multivessel percutaneous coronary intervention (PCI) in ST elevation myocardial infarction (STEMI) complicated by cardiogenic shock with multivessel disease. Methods: Using a nationwide, prospective, multi-center registry in Korea between November 2005 and September 2010, 338 patients were selected. Inclusion criteria were: 1) STEMI with cardiogenic shock and 2) multivessel disease with successful primary PCI for the infarct-related artery. Patients were divided into multivessel PCI and culprit-only PCI. Primary outcome was all-cause mortality. Results: Median follow-up duration was 208 (interquartile range: 46 to 380) days. Multivessel PCI was performed during the primary PCI in 75 (22.2%) patients. In-hospital mortality was similar in both groups (multivessel PCI vs. culprit-only PCI: 24% vs. 26.2%, p=0.696). All-cause mortality during follow-up was not significantly different between the two groups after adjusting for patient, angiographic and procedural characteristics as well as propensity scores for receiving multivessel PCI (32% vs. 30.8%, adjusted hazard ratio [HR] 1.09, 95% confidence interval [CI] 0.63-1.90, p=0.758). There were no significant differences between the groups in respective rates of major adverse cardiac events (40.0% vs. 36.5%, adjusted HR 1.07, 95% CI 0.65-1.77, p=0.778) and any revascularization (6.7% vs. 5.1%, adjusted HR 1.07, 95% CI 0.25-4.62, p=0.933). Conclusions: Multivessel PCI may not be beneficial for patients with cardiogenic shock complicating STEMI and multivessel disease during primary angioplasty.