Objective: Insulin resistance is a risk predictor for many cardiovascular diseases, but its effect on etiology and prognosis of diseases has not been clearly identified. In this study, we aimed to investigate whether admission index of insulin resistance (aIRI), recently and practically presented for determination of insulin resistance, could be a new risk predictor of early prognosis in nondiabetic acute coronary syndromes. Methods: One hundred and sixty nondiabetic patients admitted to the intensive coronary care unit and underwent coronary angiography with the diagnosis of acute myocardial infarction (AMI) (Group I; 72 patients; mean age - 58 ± 12 years) or unstable angina pectoris (UAP) (Group II; 88 patients; mean age 58 ± 10 years) were included in the study. In all patients blood glucose and insulin levels were measured on admission and AIRI was calculated by the formula of “admission glucose level X insulin level / normal blood glucose level (5mmol/L) X normal insulin level (5 mU/L)” for each patient. After determining the left ventricular ejection fraction (LVEF) and wall motion score index (LVWMSI) echocardiographically and calculating the Gensini score index from coronary angiography, the patients were followed up for major cardiac events (heart failure, atrial fibrillation, reinfarction, life–threatening ventricular arrhythmias, atrio-ventricular block, need for revascularisation and mortality) for 30 days. Results: AIRI was found higher in Group I (7.2± 5.3 versus 5.2±4.4, p< 0.01) than in Group II. AIRI was positively correlated with Gensini score and LVWMSI (r=0.41, p<0.01 and r=0.48, p<0.001, respectively) and negatively correlated with LVEF (r=-0.37, p=0.001) in Group I. In addition, it was seen that positive correlation of AIRI with Gensini score (r=0.23, p=0.01) and LVWMSI (r=0.43, p=0.0001) in Group I persisted on multivariate regression analysis. Again, AIRI was significantly correlated with heart failure (r=0.42, p<0.0001), atrial fibrillation (r=0.35, p=0.002) and reinfarction (r=0.23, p=0.04) in Group I. Along with this, in multivariate regression analysis, it was correlated with heart failure (r=0.21, p<0.007), atrial fibrillation (r=0.18, p=0.01) and reinfarction (r=0.18, p=0.01). On the other hand, there was no significant correlation between AIRI and these parameters in Group II. Conclusion: AIRI can be used in early stage as a risk predictor to determine high-risk subgroups of nondiabetic patients presenting with AMI. Also AIRI, a parameter, which is practically calculated and easily used, is an independent risk factor detecting the extent of coronary artery disease and left ventricular dysfunction in patients with AMI.