Within carotid disease, asymptomatic carotid stenosis is atherosclerotic narrowing of the internal carotid artery found before it has caused an ipsilateral stroke, transient ischaemic attack (TIA) or retinal event, often incidentally on duplex ultrasound. Its stroke risk on modern medical therapy is low and has fallen since the first surgical trials. The risk rises with the degree of stenosis and with markers of a vulnerable plaque, such as intraplaque haemorrhage, silent infarction on brain imaging, progression of the stenosis and microembolic signals on transcranial Doppler. Every patient receives intensive medical therapy, and the decision is whether carotid endarterectomy (CEA) or carotid artery stenting (CAS) adds enough to it, in a given patient, to justify its early procedural risk. Patients are followed for ipsilateral symptoms, progression of untreated stenosis and restenosis after a procedure.