Intravascular ultrasound (IVUS) is useful in evaluating coronary stent deployment. The aim of this study was to assess the safety and utility of IVUS in carotid artery stenting (CAS). Ninety-eight consecutive high-risk patients (107 arteries) underwent CAS. IVUS was performed prior to predilatation in 87 of the 107 vessels and in all 107 following stent deployment when an optimal angiographic appearance was obtained. Quantitative carotid angiography (QCA) and IVUS analysis were performed offline. Procedural success was 97%. Combined stroke or death at 30 days was 5.6%. IVUS measurements of the minimum lumen diameter (MLD) of the distal internal carotid artery (ICA) reference segment were similar to QCA (4.60 +/- 0.74 vs. 4.74 +/- 0.71 mm; P = 0.21). The ICA stent MLD was significantly smaller by IVUS compared to QCA (3.65 +/- 0.68 vs. 4.31 +/- 0.76 mm; P < 0.001). IVUS detected stent malapposition in 11%. IVUS findings, after an optimal angiographic result, necessitated additional treatment in 9% of procedures. Calcium was detected in more arteries with IVUS than angiography (61% vs. 46%; P < 0.05). Arteries with superficial lesion calcification subtending three or four quadrants by IVUS had a 31% incidence of stroke compared with a 1% incidence in arteries without severe superficial calcium (P < 0.001). We found IVUS imaging in CAS to be safe even prior to plaque dilatation. IVUS provides a more accurate assessment of stent dimensions, expansion, and apposition than angiography. Severe calcification by IVUS was associated with a higher risk of stroke.