Background : Primary percutaneous coronary intervention (PCI) is a better strategy in opening occluded coronary arteries. However, many patients are admitted to hospitals without PCI facilities. Fibrinolysis was preferred for low risk patients with early presentation, unless contraindications were present. The aim of this study was to seek predictors of urgent PCI in these fibrinolysis-preferred patients. Methods: Between Nov 2005 and Jan 2008, 411 patients treated by thrombolysis (55.0짹 10.7 years, 86.1% males) with early presentation ST-elevation myocardial infarction (STEMI) (���3 hr from symptom onset) were enrolled in a nationwide prospective Korea Acute Myocardial Infarction Registry. All patients were fibrinolysis-preferred patients who were under 75-year-old, had no contraindication of fibrinolysis, pulmonary edema and cardiogenic shock. Results: Failed fibrinolysis or threatened re-occlusion occurred in 106 patients (25.8%). The variables of the Thrombolysis In Myocardial Infarction (TIMI) risk score (age, history of diabetes, hypertension, or angina, systolic blood pressure <100 mmHg, Heart rate >100/min, Killip class II, Weight <76 kg, anterior ST elevation or complete left bundle branch block), gender and history of smoking, dyslipidemia were used for analysis. By utilizing a stepwise multivariable logistic analysis (backward elimination), anterior ST elevation or complete left bundle branch block (CLBBB) on initial electrocardiogram (ECG) was only independent predictor of fibrinolysis failure (OR 1.593, 95% confidential interval 1.002 to 2.532, p=0.047), but also of one-month mortality (OR 9.676, 95% CI 1.165 to 80.335, p=0.036). Conclusion: STEMI patients with anterior ST elevation or CLBBB on ECG should be considered for an early triage to hospitals with PCI facilities before or after fibrinolysis even in patients with low risk and early presentation.