The goal of carotid endarterectomy is to remove an obstructing or embologenic lesion and reconstruct a durable arterial segment free of flow abnormality. The technical adequacy of 250 endarterectomy sites in 235 patients was assessed at operation by pulsed Doppler spectral analysis and arteriography and was correlated with postoperative patency, the incidence of residual and recurrent stenosis, and clinical outcome. Duplex scanning was used after operation to categorize disease severity. At operation, 10 patients (4%) had angiographic and Doppler flow abnormalities identified in the internal carotid artery. Vessel exploration identified intimal flaps, platelet aggregation, or stricture. Residual flow disturbances at the endarterectomy site correlated with perioperative thrombosis and stroke, angiographic abnormalities, primary closure of the arteriotomy, and a postoperative duplex scan consistent with stenosis. In 175 patients (182 sites) with normal arterial flow after carotid bifurcation endarterectomy, no thrombotic events occurred and the incidence of recurrent stenosis (life-table analysis) was zero at 3 months, 5% at 1 year, and 9% at 2 years. The incidence of occlusion and recurrent stenosis was increased (8% at 3 months, 18% at 1 year, and 21% at 2 years) in 68 arteries with residual flow disturbance identified at operation. Assessment of endarterectomy sites for turbulence identifies anatomic lesions that threaten patency and increase the incidence of residual and recurrent stenosis.