BACKGROUND To measure by Doppler sonography the blood flow volume (BFV) of the ipsilateral and contralateral extracranial internal carotid arteries (ICAs) and both vertebral arteries (VAs) before and after a carotid endarterectomy (CEA) of the ICA. We correlated the result with the degree of stenosis of the ICA. METHODS One hundred seven patients who had a CEA were divided into 2 groups. Group I consisted of subjects with stenosis of ipsilateral ICA of >or=70% to near occlusion and Group II included subjects with near occlusion. The Doppler sonographic examinations were performed 1 day before the CEA, 7 days after the CEA, and 1 month after the CEA. The peak systolic velocity, end-diastolic velocity, time-averaged maximum blood flow velocity, resistance index of the ipsilateral ICA, and the BFV of both ICAs and both VAs were calculated. RESULTS There was a significant increase in the peak systolic velocity, maximum blood flow velocity, and the BFV of the ipsilateral ICA after the CEA. The BFV of the contralateral ICA and both VAs were not significantly altered after the CEA in both groups. CONCLUSIONS The main CEA hemodynamic effect was an increase in the BFV of the ipsilateral ICA regardless of the degree of stenosis.