Background: Despite recent success of efforts to shorten the door-to-balloon or needle time in patients with ST-segment elevation myocardial infarction(STEMI), prehospital delay remains unaffected. Nonetheless, the factors associated with prehospital delay have not been clearly identified in Korea. Methods: We retrospectively evaluated 423 patients with STEMI presented to Samsung Changwon Hospital from January 2008 to December 2010. Results: The mean symptom onset to door time of total 423 patients was 255짹285 (median: 150) minutes. The patients were analyzed in two groups according to symptom onset to door time (short delay group: ���180 min vs long delay group: >180 min). In-hospital mortality was significantly higher in long delay group compared with short delay group (6.9% vs 2.8%; P=0.048). Among demographic and clinical variables, diabetes, low educational level, triage via other hospital, use of private transport and night time onset were more frequently observed in long delay group (21% vs 30%; P=0.038, 47% vs 59%; P=0.013, 72% vs 82%; P=0.027, 25% vs 41%;P<.0001 and 33% vs 48%; P=0.002, respectively). Age and percentage of sex, history of angina and presence of family or relatives were not significantly different between two groups. In multivariate logistic regression, low education level, private transport, presence of transfer, and symptom onset during night time were significantly associated with prehospital delay (Table1). Conclusions: The present study demonstrates that prehospital delay is associated with higher in-hospital mortality. The results also suggest that low education level, private transport, triage via other hospital, and night time symptom onset are significant determinants of prehospital delay in patients with STEMI.