The aim of carotid endarterectomy is to reduce the risk of stroke and death in patients with carotid artery disease. The benefit to society of surgeons undertaking this operation lies in the balance between the risks of the natural history of the carotid disease and the risks of the surgical treatment. Carotid endarterectomy is probably the vascular surgical procedure with the most scientific evidence in its favour. In this article the reliability of evidence is graded A-C according to the classification in Box 1. The natural history of carotid disease is quite different for patients with symptomatic and asymptomatic carotid arterial stenoses. Symptomatic stenoses include those causing transient ischaemic attack and amaurosis fugax. Also included are patients who have had a previous completed stroke. Asymptomatic patients may have a significant carotid stenosis found incidentally, they may have a moderate stenosis that progresses on duplex follow-up, or finally they may have a stenosis identified as part of a routine preoperative work-up before major surgery such as coronary artery bypass grafting.