Objectives and background Early restoration of patency of the infart-related artery imporves patient survival and reduce MACE. But the impact of time-delay on prognosis in patients undergoing primary stenting still has not been clarified, so we evaluated the relationship between symptom-onset-to-balloon time and 6 month MACE in patients with ST-segment elevation myocardial infarction (STEMI) treated by primary stenting. Methods We reviewed Catholic Medical Center primary stenting registry. Our study population consisted of 103 patients with STEMI treated by primary stenting from 1998 to 2004. All patients received primary stenting within 12hr from chest pain onset Results 5 patient (4.7%) died at 6 months. Symptom-onset-to-balloon time >5hr was an independent prognostic factor of the higher MACE rate (P=0.033), together with old age and elevated creatinine level. No relationship was found between door-to-balloon time and 6 month MACE. Predictors of 6 month MACE at multivariate is showed in table Conclusion Our study revealed that, in patients with STEMI treated by primary stenting, symptom-onset-to-balloon time (>5hr), but not door-to-balloon time, was an independent predictor of 6 month MACE, together with old age and elevated creatinine level.