Purpose: Although National Cholesterol Education Program (NCEP) - Adult Treatment Panel III (ATPIII) recommends direct measurement instead of calculation for low-density lipoprotein (LDL) cholesterol determination, Friedewald formula is still frequently used in clinical practice. The objective of this study is to investigate agreement of LDL cholesterol concentrations between direct and indirect measurement by Friedewald formula in patients with acute myocardial infarction (AMI). Methods: Between November 2005 and January 2008, 8711 eligible patients (6185 males and 2526 females; mean age=65.1 짹 12.5 year-old) were included in the Korea AMI Registry. Patients with triglyceride ���400mg/dL and receiving lipid-lowering medications were excluded. Results: Direct measured LDL cholesterol (dLDL) concentrations were significantly higher than calculated LDL cholesterol (cLDL) concentrations (117.8 mg/dL versus 115.2mg/dL, p<0.001). The mean ���LDL concentration (dLDL – cLDL concentration) was 2.6짹21.7 mg/dL. The ���LDL concentrations were significantly increased according to triglyceride concentrations (figure). In multivariate linear regression analysis, the predictor of higher ���LDL concentration were systolic blood pressure, non-ST elevation MI, and higher total cholesterol and triglyceride concentrations, whereas age���65, higher high-density lipoprotein cholesterol concentration, and blood sampling obtained 2 days after admission were independent predictor of lower ���LDL concentration. Conclusions: Various clinical conditions affect the agreement of LDL cholesterol concentrations between dLDL and cLDL; therefore, the dLDL and cLDL concentrations are not interchangeable in patients with AMI.