Background: Vulnerable plaque (VP) is defined as a coronary plaque not only prone to thrombosis and/or rupture but also at risk for rapid progression. We sought to evaluate a lesion which shows rapid progression and to know clinical outcomes of intermediate lesion according to tissue type by intravascular ultrasound-virtual histology (IVUS-VH). Methods: Study subjects consisted of 98 lesions in 94 patients (61.8짹11.8 years old, 68 males) with intermediate coronary artery lesion (stenosed 30%~70%), who underwent IVUS-VH examination. Clinical follow up was done in 64 patients out of 65 eligible patients (98.5%) and follow up IVUS-VH were performed in 48 lesions/66 eligible lesions (72.7%). Results: Mean minimal luminal diameter was 1.79짹0.53mm and % diameter stenosis was 43.4짹9.05% in total study subjects. Gray scale IVUS data showed that mean minimal luminal area was 5.4짹2.1mm2, number of lesion with minimal luminal area (MLA)<4.0mm2 was 31 lesions (31.6%), and lesion length was 13.9짹7.2mm. Fibrous cap atheroma was the most common lesion type (n=42, 42.9%), followed by thin cap fibroatheroma (TCFA, n=28, 28.6%), fibrocalcific atheroma (n=17, 17.3%), and pathological intimal thickening (n=7, 7.1%). The remaining 4 lesion could not be classified. There were 3 deaths (causes; heart failure, intracranial hemorrhage, and sudden cardiac death) and 8 lesions in 7 patients showing rapid lesion progression, which required intervention during mean 8.7짹2.9months follow up period. TCFA lesion type showed higher risk of rapid lesion progression (38.5% vs. 8.6%, p=0.014) than non-TCFA lesion and lesion MLA<4.0mm2 showed also higher risk (35.3% vs. 6.5%, p=0.010) than lesion MLA���4.0mm2. The risk of rapid lesion progression requiring PCI was highest (66.7%) in those presenting with MLA<4.0mm2 and TCFA, followed by MLA<4.0mm2 or TCFA (16.7%), and lowest (4.2%) in those without the above parameters. Conclusion: This study suggests that TCFA is an important predictor for VP and TCFA can be considered with MLA by IVUS-VH.