One hundred and seventy-five carotid bifurcations have been scanned using intraoperative ultrasonic imaging. The technique is simple, reproducible, rapid, and reliable. Intimal flaps, clamp stenoses, residual plaques, and platelet accumulations were detected by this method. Most technical defects occurred in the external carotid artery (12%), and it is recommended that significant lesions remaining in this vessel should be removed. Defects in the internal carotid artery and common carotid artery were much less common (7%) and most of these were quite small, not requiring reopening. In fact, only 2% required reopening. In 1% of patients there were defects detected that led to stroke, which would have been removed on present criteria. Although there were other causes of stroke, technical error remains an immediately reversible source of postoperative stroke that can be avoided by the use of operative ultrasonic imaging. Long-term minor defects, as followed by noninvasive tests, rarely became significant and bore no relationship to the development of restenosis.