We aimed to assess the risk factors and outcome of ventricular fibrillation (VF) before and duringprimary percutaneous coronary intervention (PPCI) in patients with ST-segment elevationmyocardial infarction. From 1999 to 2012, we consecutively enrolled 5,373 patients withST-segment elevation myocardial infarction. In total, 410 of the patients had VF before and 88had VF during PPCI. During a mean follow-up of 4.2 years, 1,196 subjects died. A logisticregression model identified younger age, anterior infarct, Killip class >I at admission, and apreprocedural Thrombolysis In Myocardial Infarction flow grade of 0 to I to be significantlyassociated with VF before PPCI, whereas inferior infarct, a preprocedural Thrombolysis InMyocardial Infarction flow grade of 0 to I, and Killip class >I at admission were significantlyassociated with VF during PPCI. All-cause mortality was evaluated using the Cox regressionmodel. Compared with the patients without VF, those with VF before or during PPCI had asignificantly increased 30-day mortality, with an adjusted hazard ratio [ 3.40 (95% confidenceinterval 1.70 to 6.70) and 4.20 (95% confidence interval 1.30 to 13.30), respectively. Importantly,there was no tendency of 30-day mortality difference between VF before and during PPCI (p [0.170). In patients with VF before or during PPCI who survived for at least 30 days, there was noincrease in the long-term mortality. In conclusion, our data suggest that 30-day mortality is thesame for patients with VF before PPCI compared with VF during PPCI, and the occurrence of VFbefore or during PPCI was associated with increased 30-day mortality but not with long-termmortality.