Background: Dyslipidemia is a well-known risk factor for the development of coronary artery disease. But, the relation between the low-density lipoprotein (LDL) cholesterol level and clinical outcome after percutaneous coronary intervention (PCI) in patients with acute myocardial infarction (AMI) has not been described. Methods: 9,571 eligible patients (mean age 62.6 짹 12.5 years, 6,967 men) who underwent PCI with a final diagnosis of AMI from the Korea AMI Registry were divided into five groups according to the LDL cholesterol level : < 70, 70-99, 100-129, 130-159 and ��� 160 mg/dL. The clinical outcomes at hospital, 1 month and 12 months after PCI in patients with AMI were examined. Results: Mean LDL cholesterol levels were 116 짹 40 mg/dL in men and 123 짹 49 mg/dL in women (p < 0.001). Age and comorbidities decreased as the LDL cholesterol increased. Patients with higher LDL cholesterol levels had favorable hemodynamic status and laboratory findings. Life-saving medications including lipid lowering drug were underused in patients with lower LDL cholesterol level. During the 12 month follow-up, we registered 1,172 in-hospital complications (12%), 478 composite major cardiac events at 1 month (6%) and 473 deaths at 12 months (6%). The clinical outcomes at hospital, 1 month and 12 months after PCI showed better results as the LDL cholesterol increased, except for patients with LDL cholesterol ��� 160 mg/dL: 20%, 14%, 12%, 9% and 10% of in-hospital complications, 12%, 6%, 5%, 4% and 5% of 1 month major cardiac events, and 14%, 7%, 6%, 4% and 6% of 12 month deaths (all p<0.001) occurred from group I to V, respectively. In a Cox proportional hazard model, LDL cholesterol level was not an independent predictor of mortality at 12-month after adjusting clinical characteristics including demographics and biologic data. Conclusions: The cholesterol paradox in patients with AMI is related to confounding by baseline characteristics associated with survival. More intensive treatment including lipid lowering therapy for AMI in patients with lower LDL cholesterol level may result in a better clinical outcome.