Clinicians have long used the size of the lumen and the angiogram as a predictor of coronary events. However, cardiovascular disease is not a disease of the lumen but a disease of the vessel wall. In early stages, atherosclerosis outwardly remodels the external elastic membrane; only late in the disease process does luminal narrowing occur, enabling angiographic detection. This has profound implications for drug therapy, because approximately 70% of patients present with acute myocardial infarction (MI) or sudden death, not angina as the first symptom of coronary disease. Intravascular ultrasound (IVUS) can provide detailed images of the artery and is the only technique currently available that enables physicians to routinely visualize coronary plaques. Due to its sensitivity in measuring plaque volume and content, IVUS may be a useful surrogate marker to evaluate the atherosclerotic process in smaller numbers of patients than required for conventional clinical endpoint trials.