Coronary heart disease remains a leading cause of morbidity and mortality. Surrogate imaging endpoints may allow smaller sample sizes and shorter study durations to expedite the process of drug development and testing, and to evaluate potential benefits of novel antiatherosclerotic drugs before clinical endpoint data are available - an approach that may reduce cost and effort. Intravascular ultrasound (IVUS) is particularly suitable because it is readily available and because of its relatively high image resolution, accurate and reproducible measurements, ability to detect mild, angiographically silent atherosclerotic disease that can be a precursor of future coronary events, and suitability for serial (baseline and follow-up) imaging and analysis. However, there are significant limitations to the use of IVUS as an endpoint in progression/regression studies that must be considered when evaluating the results of such studies. (Circ J 2009; 73: 1557-1560)