BACKGROUND: The relationship between insulin resistance (IR) and plaque components in patients with coronary artery disease is not well understood. We hypothesized that patients with IR would have higher amount of necrotic core in plaque component. METHODS: A total of 149 patients (103 males) with coronary artery disease who underwent coronary angiography with virtual histology-intravascular ultrasound (VH-IVUS) were analyzed. The region of interest (ROI) was the most diseased 10mm segment of a single coronary artery. The IR index was determined from fasting plasma glucose and insulin concentrations, using quantitative insulin sensitivity check index (QUICKI) and calculated by using the formula; 1 / (log insulin (microU/mL) + log glucose (mg/dL)). IR was defined as QUICKI ��� 0.33. VH-IVUS classified the color-coded tissue into four major components: fibrotic, fibro-fatty, necrotic core (NC) and dense calcium. RESULTS: The patients with IR (n = 68) had significantly greater total plaque burden (119.5 짹 49.9 mm3 vs 100.6 짹 41.3 mm3, p = 0.012) and the amount of NC (21.2 짹 15.7 mm3 vs 16.1짹 12.5 mm3, p=0.030) at ROI than patients without IR. At minimal lumen diameter (MLD), total plaque burden was tended to be greater (12.3 짹 5.8 mm2 vs.10.7 짹 4.4 mm2, p = 0.070) and the amount NC was significantly greater (2.2 짹 1.8 mm2 vs 1.6 짹 1.1 mm2, p = 0.017) in patients with IR. Significant negative correlation was observed between QUICKI and the amount of NC at ROI (r = -0.202, p = 0.013). Similarly significant positive correlation was observed between HbA1C and body mass index and the amount of NC at ROI (r = 0.292, P < 0.00, r = 0.240, p = 0.003). Neither the low-density lipoprotein cholesterol nor non high-density lipoprotein cholesterol were associated with the volume of NC at ROI and the amount of NC at MLD. CONCLUSIONS: Metabolic parameters are associated with the amount of NC in plaque components contributing to the increasing risk of plaque vulnerability in patients with coronary artery disease.