BACKGROUND: Carotid artery stenosis is a late complication of radiotherapy to the neck region. This complication has, however, a significant impact with increased risk of stroke causing mortality and morbidity. Clinicians' awareness of this complication and early detection is therefore important. METHODS: Eighty patients with nasopharyngeal carcinoma (NPC) who had received radiotherapy were recruited for color Doppler ultrasonography of the carotid arteries. fifty-eight patients with newly diagnosed NPC who had never received any radiotherapy were recruited as controls. All patients with significant carotid stenosis were referred to the neurology clinic for further assessment. RESULTS: Twenty-four patients were found to have more than 50% diameter reduction in the extracranial carotid artery. Clinical assessment by a neurologist showed 9 of 24 patients had a history of transient ischemic attack, amaurosis fugax, or stroke. Seven of these patients had clinically detectable neck bruit. CONCLUSIONS: Clinicians attending to patients after radiotherapy for head and neck cancers should be aware of this long-term complication of radiotherapy. A detailed clinical history and incorporation of auscultation of carotid arteries in routine follow-up of postradiotherapy patients are recommended.