Background: The aims of this study were to determine the interactive effect of symptom-to-door (STD) time and door-to-balloon (DTB) time on 12-month mortality in patients undergoing primary percutaneous coronary interventions (PCI) for ST-segment elevation myocardial infarction (STEMI). Methods: Between November 2005 and January 2008, 3,108 eligible patients (2,307 men; mean age = 61.8 짹 12.6 years-old) who had an STEMI with an STD time of 12 hours and underwent primary PCI were analyzed from the Korea Acute MI Registry. Patients were stratified into 4 groups based on STD time (<3 versus ���3 hours) and DTB time (<90 versus ���90 minutes). The cutoff points of 3 hours for STD time and 90 minutes for DTB time were chosen after preliminary analyses of the relation between STD time and mortality and DTB time and mortality. Results: The patients with a STD time of <3 hours and DTB time of <90 minutes had the lowest 12-month mortality (5.9%). Patients with a STD time of <3 hours and DTB time ���90 minutes and had significantly greater mortality than patients with an STD time of <3 hours and DTB time of <90 minutes (hazard ratio [HR] 1.866, 95% confidence interval [CI] 1.010 to 3.447, p=0.046), as did patients with a STD time of ���3 hours and DTB time of <90 minutes (adjusted HR 1.957, 95% CI 1.040 to 3.681, p=0.037) after adjustment for clinical and angiographic variables in Cox proportional hazards model. The patients with a STD time of ���3 hours and DTB time of ���90 minutes had the highest 12-month mortality compared to patients with an STD time of <3 hours and DTB time of <90 minutes after adjustment for clinical and angiographic variables (adjusted HR 2.554, 95% CI 1.388 to 4.700, p=0.003), and after adjustment for clinical, angiographic, and discharge medications (adjusted HR 2.217, 95% CI 1.015 to 4.843, p=0.046). Conclusion: This observational study suggest the combination of short (<3 hours) OTD time short (<90 minutes) DTB time are associated with the lowest 12-month mortality in patients with STEMI.