Background: Intra-aortic balloon pump therapy (IABP) in ST-segment elevation myocardial infarction (STEMI) with cardiogenic shock (CS) is recommended in the current guidelines. However, there is no randomized evidence for a survival benefit. Therefore, we investigated the clinical outcomes of patients with an acute MI complicated by CS undergoing percutaneous coronary intervention (PCI) with or without the use of an IABP. Methods: Between November 2005 and January 2008, 281 CS patients (177 men; mean age = 67.2 짹 11.3 years-old) who had an STEMI with a symptom-to-door time of 12 hours and underwent primary PCI were analyzed from the Korean acute MI registry. We compared in-hospital mortality of 145 patients managed with PCI and IABP, compared to 136 patients who were managed with PCI without an IABP. Results: Patients managed with IABP compared to no IABP had a significantly lower systolic blood pressure, higher Killip class, higher serum glucose levels, lower levels of total cholesterol and high-density lipoprotein cholesterol, higher culprit vessel of left main and left anterior descending artery, and lower inferior MI. Patients managed with IABP received significantly lower optimal medical therapy including antiplatelet agents, beta-blockers, angiotensin-converting enzyme inhibitors/ angiotensin II receptor blockers, and lipid lowering agents during hospitalization. In univariate analysis, use of an IABP was associated with increased in-hospital mortality (59.5% versus 45.2%, p=0.017). In multivariate logistic regression model, use of an IABP (OR 1.961, 95% CI 1.110–3.462; p=0.020) was an independent predictor of in-hospital mortality in addition to age (OR 1.055, 95% CI 1.023–1.087; p=0.001) and diabetes mellitus (OR 2.125, 95% CI 1.191–3.794; p=0.011) after adjustment for clinical and angiographic variables. However, use of an IABP (OR 1.212, 95% CI 0.614–2.394; p=0.579) was not an independent predictor for in-hospital mortality after adjustment for optimal medical therapies in fully adjusted model. Conclusions: Patients undergoing PCI complicated by CS remain a high-risk group associated with significant mortality. The use of an IABP was not an independent predictor of in-hospital mortality in this multicenter observational cohort. However, despite use of IABP, utilizing contemporary PCI techniques was associated with poorer outcomes. Further studies testing efficacy of more intensive medical therapy and invasive procedures such as emergency bypass system are required in this critical clinical setting.