OBJECTIVES: This study was designed to identify potential differences between the intravascular ultrasound (IVUS) characteristics of spontaneously ruptured and nonruptured coronary plaques. BACKGROUND: The identification of vulnerable plaques in vivo may allow targeted prevention of acute coronary events and more effective evaluation of novel therapeutic approaches. METHODS: Intravascular ultrasound was used to identify 29 ruptured plaques in arteries containing another nonruptured plaque in an adjacent segment. Intravascular ultrasound characteristics of these plaques were compared with plaques of computer-matched controls without evidence of plaque rupture. Plaque distribution was assessed by measuring the eccentricity of lumen location (inside the total vessel). Lumen cross-sectional area narrowing was calculated as [1 -(target/reference lumen area)] × 100%. A remodeling index was calculated as lesion/reference arterial area (>1.05 = compensatory enlargement, <0.95 = shrinkage). RESULTS: Among the three groups of plaques, there was no significant difference in quantitative angiographic parameters, IVUS reference dimensions and IVUS lumen cross-sectional area narrowing. There was a difference in plaque distribution; lumen location by IVUS was significantly more eccentric in ruptured than in nonruptured (p = 0.002) and control plaques (p < 0.0001). The arc of disease-free vessel wall was larger in ruptured than in control plaques (p < 0.0001). The remodeling pattern of ruptured and nonruptured plaques differed significantly from that of the control plaques (p = 0.0001 and 0.003); compensatory enlargement was found in 66%, 48%, and 17%, whereas shrinkage was found in 7%, 10% and 48%, respectively. CONCLUSIONS: Intravascular ultrasound assessment of plaque distribution and vascular remodeling may help to classify plaques with the highest probability of spontaneous rupture.