We investigated the relationship between no-reflow and pre-intervention intravascular ultrasound (IVUS) findings in 84 pts with angiographic evidence of target lesion thrombus (angiographic generalized haziness or filling defect) within native arteries undergoing percutaneous coronary intervention (PCI) without a distal protection device. Angiographic no-reflow was defined as post-PCI TIMI flow grade 0~2. IVUS assessment included (1) morphological characteristics of thrombus (scintillating appearance, lobulated mass, distinct interface between the suspect thrombi and plaque, or microchannels within a lobulated mass), (2) thrombus mobility, and (3) presence of attenuated plaque (plaque with deep echo attenuation, but without calcification). Results: There were no serious IVUS-imaging related procedural complications in these pts with angiographic thrombus. IVUS identified thrombus in 76 lesions (90.5%): scintillation in 45.2%, lobulated mass in 64.3%, distinct interface in 10.7%, microchannels in 8.3%, mobility in 26.2%, and attenuated plaque in 44%. Most attenuated plaques (88.9%) were detected at the minimal lumen area site. No-reflow was observed in 35 lesions post-PCI (41.7%). In general, IVUS features of thrombus were significantly more common in lesions that developed no-reflow (Table); multivariate logistic regression analysis showed that attenuated plaque (p=0.012; OR, 6.04; 95% CI, 2.33~15.70) and thrombus mobility (p<0.0001; OR, 31.33; 95% CI, 6.54~149.93) were independent predictors of post-PCI no-reflow in angiographic thrombus-containing lesion. Intrastent plaque prolapse was more frequen in pts with attenuated plaque (66.7% vs.18.4%, p<0.001) Conclusions: IVUS imaging of angiographic thrombus-containing target lesions is safe. In lesions IVUS findings of mobility and attenuated plaque predict no-reflow; and the use of distal protection should be considered.