BACKGROUND AND OBJECTIVES: Early studies indicate that cholesterol levels decrease significantly after acute myocardial infarctions (AMI). However, most studies did not measure low-density lipoprotein cholesterol (LDL-C) directly. More recent studies suggest less pronounced changes in cholesterol levels after AMI. We investigated acute change in the lipid profile immediately following AMI, and evaluated clinical utility of direct measurement of LDL-C levels during hospitalization for AMI. METHODS: Forty-three patients (33 males and 10 females; mean age=61.8 짹 12.0 year-old) admitted for AMI were included in this study. Lipoprotein levels were measured at admission (fasting or nonfasting), at Day 1 (fasting), and at Day 2 (fasting) after admission. RESULTS: Of 43 patients, 7 (16.3%) had a history of dyslipidemia, and no patients were taking lipid-lowering drugs at the time of admission. The total cholesterol and measured LDL-C levels decreased significantly at Day 1 after admission (-18.7mg/dL (-8.9%) and -12.4mg/dL (-5.5%), respectively, p<0.05), and seemed to increase slightly at Day 2, but the mean changes were not significant (-5.7mg/dL (-4.1%) and -7.0mg/dL (-2.0%), respectively). There were no significant changes in high-density lipoprotein cholesterol (HDL-C) levels and triglyceride levels within 48 hours after an AMI. When LDL-C were calculated using the Friedwald equation, there were no significant changes in calculated LDL-C levels at Day 1 (-4.4mg/dL (0.0%)) and at Day 2 (-5.1mg/dL (-1.1%)). Calculated LDL-C levels were significantly lower than measured LDL-C levels at admission, Day 1, and Day 2. When LDL-C were measured directly at the time of admission, 79.1% of 43 patients met the National Cholesterol Education Program (NCEP) guidelines for drug therapy (LDL-C ���100mg/dL) compared with 61.3% at Day 1 and 66.7% at Day 2. When LDL-C was calculated at the time of admission, 54.5% of 43 patients met the NCEP guidelines for drug therapy compared with 53.3% at Day 1 and 61.5% at Day 2. CONCLUSIONS: Mean total cholesterol and LDL-C levels decrease within 48 hours after an AMI, but these changes were not significant and can be used to guide selection of lipid-lowering medication.