To evaluate the effect of intraoperative duplex scanning (IDS) on the incidence of perioperative and postoperative strokes as well as residual and recurrent stenosis, we reviewed 141 patients who underwent 152 consecutive carotid endarterectomies (CEAs) between July, 1990 and June, 1995. Follow-up of 129 cases, with a mean follow-up of two years, revealed no perioperative deaths and three strokes for a combined perioperative stroke-death rate of 2.3 per cent. In 50% (64 of 129) of the CEAs, intraoperative duplex scans were obtained based on the attending surgeon's preference. We noted that the incidence of residual stenosis (>50% stenosis on the first duplex after CEA) was significantly lower in those undergoing IDS (3/64) versus those without IDS (13/65) (P < 0.05; risk ratio 0.31; 95% confidence interval 0.11, 0.91). IDS resulted in a modification of the internal carotid reconstruction in 9 per cent (6 of 64) of the cases with no resulting postoperative strokes or residual/recurrent stenosis. There was no significant difference in the frequency of recurrent stenosis (>50% stenosis after a normal duplex) in the two groups (3 of 64 with vs 2 of 65 without). Of patients not undergoing intraoperative scanning, four underwent redo CEA for symptomatic residual stenosis due to a retained intimal flap in the internal carotid artery. There were three strokes observed within 30 days of the initial CEA, all of which occurred in patients who did not undergo IDS at their initial operation. We conclude that IDS can identify technical defects following internal carotid reconstruction, thereby reducing the incidence of both residual stenosis and postoperative morbidity in patients undergoing CEA.