Background: Several studies have demonstrated that the low-density lipoprotein cholesterol/high-denisty lipoprotein-cholesterol (LDL-C/HDL-C) ratio is an excellent predictor of cardiovascular disease. The aim of the present study was to determine whether the LDL-C/HDL-C ratio would affect outcome in patients after percutaneous coronary intervention (PCI). Methods and Results: Six-hundred-eighty-seven participants who underwent successful PCI for acute coronary syndromes or stable angina were enrolled. They were divided into 3 groups on the basis of the LDL-C/HDL-C ratio recorded 6 months after PCI: those with LDL-C/HDL-C≤1.5 (n=125); 1.5<LDL-C/HDL-C≤2.0 (n=205); LDL-C/HDL-C>2 (n=357). In the 3 groups, the incidence of major adverse cardiac events (MACE) was measured during the 5 years after baseline evaluation. MACE was defined as cardiac death, non-fatal myocardial infarction, new lesions, and restenosis. The median follow-up duration was 33 months. Kaplan-Meier analysis demonstrated that patients with LDL-C/HDL-C≤1.5 had a significantly lower incidence of MACE after PCI than patients with 1.5<LDL-C/HDL-C≤2.0 (P=0.014) or with LDL-C/HDL-C>2.0 (P<0.001). In addition, Cox proportional hazards analysis indicated that the LDL-C/HDL-C ratio was correlated with the incidence of MACE (HR=1.39, 95% confidence interval: 1.20-1.61, P<0.001). Conclusions: The LDL-C/HDL-C ratio had an impact on long-term outcome in patients undergoing PCI. (Circ J 2011; 75: 905-910)