Intravascular ultrasound provides high resolution cross-sectional images of vessel walls and may help to characterize atherosclerotic plaque morphology subtypes. This new imaging modality may have an important role in assessing the results of standard and investigational interventional therapeutic procedures. Four case histories of patients with coronary artery disease treated with different catheter-based therapies are presented. In each case, intravascular ultrasound added diagnostic information unobtainable from standard radiographic imaging techniques. These cases, involving PTCA (balloon dilatation), directional coronary atherectomy, high-speed rotational ablation, and balloon-expandable stent implantation, each represent an interesting example of procedure success or failure that could not be fully discerned without the use of intravascular ultrasound. Specifically, the distribution of intramural dissection, the presence and magnitude of intracoronary calcification, and morphologic patterns of intimal hyperplasia leading to restenosis, were accurately identified by ultrasound images. Thus intracoronary ultrasound imaging significantly enhances the understanding of failure modes, success, and complications after therapeutic interventions in patients with complex coronary disease.