An intravascular ultrasound study was performed in a patient, to assess the anatomy of aortic coarctation and the results obtained after percutaneous dilation with a balloon catheter. Intravascular ultrasound imaging provides important additional information, not obtainable with other diagnostic procedures, regarding aortic wall structure and thickness. After balloon dilation, aortic disruption was clearly observed, accounting, together with the stretching of the outer layers of the aortic wall, for the increase in aortic luminal area. Intravascular ultrasound permitted also the accurate assessment of the improvement obtained. Intravascular imaging was clearly superior not only to conventional angiography, but also to transesophageal echocardiography in detecting the mechanism of dilation. We conclude that ultravascular ultrasound, with the additional information that it provides, may help in the selection of patients for percutaneous dilation of the coarctation as well as contributing to the identification of the mechanism of dilation.