Objective To examine the relationship between coronary arterial remodeling and clinical presentation. Methods A total of 34 patients with acute (10 with recent myocardial infarction and 24 with unstable angina) and 26 with stable (8 with old myocardial infarction and 18 with stable angina) coronary syndrome underwent intravascular ultrasound (IVUS) before intervention. Target lesions were classified as soft or hard plaques. Q uantitative measurements of cross-sectional area (CSA) of extal elastic memb rane (EEM), lumen and plaque were performed at the lesion site and at the proxim al and distal reference sites. Remodeling index (RI) was expressed by the ratio of EEM CSA at the lesion site to the mean EEM CSA of both proximal and distal r eference sites. Positive remodeling was defined as RI>1.05 and negative remode ling as RI<0.95. Results Soft plaque was observed more frequently in acute than in stable coronary syndrome (59% vs 31%), whereas hard plaque was more common in stable coronary syndrome (69% vs 41%) (P=0.03). The EEM CSA (15.11±2.89 mm2 vs 13.25±3.10 mm2, P=0.019) and plaque CSA (10.83±2.62 mm2 vs 9.30±2.84 mm 2, P =0.035) were significantly greater at target lesions in patients with acute r ather than stable coronary syndrome, while lumen CSA and percent area stenosis w ere similar in both groups. RI was significantly higher (1.08±0.16 vs 0.95 ±0.14, P=0.002) and positive remodeling was more frequent in acute corona ry syndrome (53% vs 23%, P=0.019), whereas negative remodeling was more com mon in stable coronary syndrome (58% vs 24%, P=0.007). Conclusions The study indicates that clinical characteristics of patients with coronary artery disease depend largely upon underlying types of coronary arterial remodeling .