Background: Increased neutrophil count has been associated with adverse clinical outcome after acute myocardial infarction (AMI). However, the association of neutrophil count with the infarct size and left ventricular dysfunction remains controversial. We investigated the relationship between infarct size after AMI and neutrophil counts on admission. METHODS: 164 consecutive patients with AMI were included in the study. Total white blood cell (WBC), neutrophil counts, creatine kinase-myocardial band (CKMB), and cardiac troponin T (cTnT) were obtained on admission and daily during the first 72 h after a patient's arrival. Echocardiographic studies were performed at a median interval of 3 days (range, 2-4 days) after the AMI. The regional wall motion score(RWMS)s were calculated. RESULTS: Neutrophil counts on admission were positively correlated with peak CKMB, peak cTnT, LV ejection fraction, and RWMS (P=0.8, P=0.01, P=0.001 and P<0.001, respectively).The most significant relationship was between basal neutrophil counts and RWMS (P<0.001). Overall, the correlation coefficients with RWMS was better than those with peak CKMB and cTnT levels for neutrophil counts. CONCLUSION: The neutrophil counts correlated with enzymatic and echocardiographic infarct size. Measuring basal neutrophil counts may be considered as an alternative biomarker to predict infarct size.