Intraoperative completion studies of the internal carotid artery following carotid endarterectomy are recommended to ensure technical perfection of the repair. Transit time ultrasound flowmeter does not require trained technicians, requires less time than other completion studies such as duplex ultrasonography and contrast arteriography, and is noninvasive. Flowmetry was compared with duplex ultrasonography and contrast arteriography to determine if the relatively simpler flowmetry could replace these two more widely accepted completion studies in the intraoperative assessment of carotid endarterectomy. Comparative intraoperative assessment was performed in 116 carotid endarterectomies using all three techniques between December 1, 2000 and November 30, 2003. Eversion endarterectomy was performed in 51 cases and standard endarterectomy with prosthetic patching in 65 cases. Patients underwent completion flowmetry, duplex ultrasonography, and contrast arteriography studies of the exposed arteries, which were performed by vascular fellows or senior surgical residents under direct supervision of board-certified vascular surgeons. Duplex ultrasonography surveillance was performed 1 and 6 months postoperatively and annually thereafter. Mean follow-up was 18 months (range, 6-42 months). The combined ipsilateral stroke and death rate was 0%. The mean internal carotid artery flow using flowmetry was 249 mL/min (range, 60-750 mL/min). Five (4.3%) patients had flow < 100 mL/min as measured with flowmetry, but completion contrast arteriography and duplex ultrasonography were normal and none of the arteries were re-explored. One carotid endarterectomy was re-explored based on completion duplex ultrasonography that showed markedly elevated internal carotid artery peak systolic velocity (> 500 cm/sec); however, exploration was normal and completion flowmetry and contrast arteriography were normal. Duplex ultrasonography studies revealed internal carotid artery peak systolic velocities > 150 cm/sec in 15 patients, but flowmetry and contrast arteriography were normal in all 15 cases and none of the arteries were re-explored. There was no correlation between flow rates measured using flowmetry and peak systolic velocities measured using duplex ultrasonography. One abnormal contrast arteriogram showed an intimal flap that was revised, but duplex ultrasonography and flowmetry were normal. Severe recurrent internal carotid artery stenosis developed in 2 patients at 6 and 9 months, but all 3 completion intraoperative studies at the time of the original operation were normal. Based on these results, wide variability in flowmetry values limits its potential usefulness to detect non-flow-limiting lesions and replace contrast arteriography or duplex ultrasonography as an intraoperative carotid endarterectomy completion study. Duplex ultrasonography was also of limited to no value, whereas contrast arteriography rarely documented a lesion that required repair.