OBJECTIVE This study examines the current role of diagnostic tests done before carotid endarterectomy and the need for routine arteriography. METHODS We prospectively studied vascular surgeons' decision-making over a 29-month period during which 111 carotid arteries in 103 patients were considered for endarterectomy. For each case the surgeon's management plan was recorded after clinical evaluation and review of the duplex scan findings, but before arteriography. This plan was later compared with the patient's ultimate clinical management. RESULTS Of 111 total cases in this period, 17 were excluded from analysis because arteriography was not done or it was performed before the surgeon's evaluation. Carotid duplex scans were diagnostic in 87 (93%) of the remaining 94 cases. The carotid lesion was incompletely assessed by duplex scanning in seven patients because the disease was not limited to the distal common or proximal internal carotid artery (n = 4); anatomic or pathologic features of the carotid artery interfered with imaging or accurate Doppler assessment (n = 1); or an internal carotid artery occlusion could not be distinguished from a high-grade stenosis (n = 2). When a technically adequate duplex scan showed significant disease of the carotid bifurcation, arteriography contributed information that affected clinical management in only a single case (1%). This patient had a middle cerebral artery occlusion distal to a high-grade carotid bifurcation stenosis. CONCLUSIONS Clinical assessment and duplex scanning were sufficient for the preoperative evaluation of 93% of the candidates for carotid endarterectomy. Clinical circumstances or atypical duplex scan findings can be used to identify the minority of patients for whom arteriography is necessary. On the basis of this experience, we have developed practical guidelines for the selective use of arteriography before carotid endarterectomy.