Intravascular ultrasound (IVUS) imaging of coronary arteries has recently become possible in vivo with the improvements achieved in the miniaturisation of ultrasound transducers. IVUS provides informations complementary to angiography, and is considered as the gold standard for the assessment of lumen size, plaque thickness and plaque distribution. As formerly demonstrated by pathological studies, IVUS also reveals an underestimation of plaque thickness with angiography and an incomplete assessment of the true morphologic distribution of the plaque burden. Among its clinical applications, IVUS can be used to monitor revascularisation procedures, and may provide very accurate measurements of progression or regression of coronary atherosclerosis and of the extent of posttransplant vasculopathy. IVUS was employed successfully to assess and optimize the results of percutaneous transluminal coronary angioplasty. Clinical studies have shown that the risk of restenosis is inversely proportional to the size of the postprocedural lumen. With the guidance of percutaneous transluminal angioplasty by IVUS, balloon size and inflation pressures were increased, and better results were obtained with larger lumen size in comparison to the results of the procedures assessed by angiography alone. These improvements contributed to abandon the anticoagulation after stent implantation in most cases. In spite of the valuable information provided by IVUS, its role in clinical settings should still be defined IVUS prolongs the revascularisation procedure and enhances its costs and risks. Thus, the cost effectiveness of IVUS in its clinical application should be determined by prospective studies.