BACKGROUND: Guidelines recommend on-site cardiac surgery backup (CSB) when percutaneous coronary intervention (PCI) is performed. However, controversy still exists as to whether PCI should be expanded to hospitals without CSB. We performed a study to compare outcomes for patients with acute myocardial infarction (AMI) undergoing PCI who were treated at hospitals without and with onsite CSB. METHODS: We analysed the Korea Acute Myocardial Infarction Registry (KAMIR) between 2005 and 2008. All patients were followed in one hospitals where they had a PCI procedure. Main outcome was defined cardiac mortality during 1 year. Hospitals with onsite CSB were initially identified based on whether they perform at least 1 CABG operations within 2 years. The database of Health Insurance Review and Assessment Service (HIRA) were used to characterize and identify the hospitals included in our study. We used the HIRA���s statistics as well as internet and telephone searches, to identify any errors or changes in hospital identifiers that could have misclassified institutions. RESULTS: In study period, a total of 10,190 patients were included; 941 patients (9.2%) in 11 hospitals without on-site CSB and 9,249 patients (90.8%) in 40 hospitals with on-site CSB. Baseline and clinical characteristics such as age, sex, cardiac risk factors were showed no significant difference between the two groups (Table 1). Survival rate of 0, 1, 6, 12 months by Kaplan-Meyer survival analysis were no significant difference between the two groups (p=0.09). There were no differences for emergent bypass surgery rate and subsequent revascularization rate, and thrombolytic therapy rate. CONCLUSION: No differences between with on-site CSB and without on-site CSB centers were found in in-hospital/30-day mortality, 1-year mortality or subsequent revascularization.