Background: The relationship between clinical outcomes after acute MI and renal function by glomerular filtration rate (GFR) is not well defined in patients with normal or mildly elevated serum creatinine level. Methods: As part of Korean Acute Myocardial Infarction Registry (KAMIR), 6834 acute MI patients with serum creatinine ��� 2.0mg/dl were enrolled in this study from November 2005 to December 2006. The renal function was stratified arbitrary to 5 groups as follows: 1) normal renal function, >90; 2) preserved renal function, 75.0 to 89.9; 3) mild renal dysfunction, 60.0 to 74.9; 4) moderate renal dysfunction, 45 to 59.9; 5) severe renal dysfunction, <45 ml/min/1.73m2. Clinical characteristics, the utilization of treatments and outcome data were analyzed and compared according to renal function. The mean follow-up duration was 419짹131 days. Results: Prevalence of older age, comorbidities, heart failure (Killip class > I), complications were increased with declining renal function (p<0.05). Reperfusion and medical therapies were underused (p<0.05) and in-hospital mortality was increased remarkably (p<0.05) with advance of renal dysfunction. The increased risks of long-term mortality and adverse events were demonstrated even in patients with mild renal dysfunction as compared with normal renal function (p<0.001). After adjustment with confounding factors, severe [odds ratio (OR): 5.3, confidence interval (CI): 2.1 to 16.1, p=0.014] and moderate (OR: 3.1, CI: 1.4 to 7.9, p=0.009) renal dysfunctions were important risk predictors of in-hospital mortality. Only severe renal dysfunction was significant risk predictor in long-term mortality (hazard ratio: 6.4, CI, 2.9 to 14.8, p=0.008). Conclusion: Spectrum of renal function, when it was presented by GFR, is broad and is important risk predictor for adverse outcomes after acute MI even in patients with normal or mildly elevated value of serum creatinine.