OBJECTIVE: Increased plasma fibrinogen level is associated with adverse events in patients with acute STsegment elevation myocardial infarction. However, the exact pathophysiologic mechanism is unknown. In this study, we evaluated the association between admission plasma fibrinogen level and reperfusion response to fibrinolytic therapy. MATERIAL AND METHODS: The study included 128 patients (79 males, 49 females; mean age 56.3 ±7.4 years) who received fibrinolytic therapy within the first 12 hours of symptom onset for acute ST-segment elevation MI. Venous blood samples were obtained to determine admission plasma fibrinogen level and subsequently, fibrinolytic therapy administered. Coronary angiography was performed within the first 72 hours and the TIMI frame count was measured for the infarct-related artery. TIMI frame counts of <40 and ≥40 were defined as complete and incomplete reperfusion, respectively. RESULTS: Complete reperfusion was achieved in 52 patients (40.6%) and reperfusion incomplete in 76 patients (59.4%). Patients with complete reperfusion had a significantly lower admission plasma fibrinogen level compared to those with incomplete reperfusion response (322±26.4 mg/dl vs 498±36.8 mg/dl; p=0.006). Increased admission fibrinogen level was an independent predictor of incomplete reperfusion response to fibrinolytic therapy (OR=4.8, %95 CI 1.2-17.3; p<0.0001) CONCLUSIONS: Higher plasma fibrinogen level is associated with both insu icient reperfusion response to fibrinolytic therapy and poor prognosis.