Pathologic studies have revealed that coronary arteries undergo compensatory enlargement in the presence of atherosclerosis. In order to assess coronary artery remodeling in vivo, we used intravascular ultrasound to examine 46 patients (36 men and 10 women; aged 58.2 ± 6.8 years) with non-calcified plaques. The vessel, lumen, and plaque areas of the atherosclerotic and of normal proximal and distal segments were determined. A total of 92 atherosclerotic segments were analyzed. The degree of stenosis ranged from 9.2 to 92.8% (mean 34.1 ±16.9%) and the plaque area from 2 to 19.6 mm2 (mean 6.3 ± 3.6 mm2). The vessel area of the atherosclerotic segment (mean 20.4 ± 7.3 mm2) was larger than that of the proximal segment (mean 18.7 ± 7.3 mm2, P = 0.018). The vessel area increased in proportion to plaque area. This relationship can be described using the equation y = 23.5(1 -e -0.35x). The difference between the vessel area in the atherosclerotic segment and that in the proximal normal segment correlated with the percentage of stenosis (r = 0.53, P Conclusion This study indicates that coronary artery remodeling, previously observed in pathologic studies, can be evaluated using intravascular ultrasound in vivo. As a result of the compensatory enlargement of the vessel, coronary angiography cannot be used to detect or exclude the early signs of coronary atherosclerosis.