Patients treated for head and neck tumours with local radiotherapy (RT) on the neck harbour an increased risk of stroke. This may be due to accelerated atherosclerotic changes within the RT-field; however, the real impact of local RT on the carotid artery remains debatable. The aim of the present study was to assess the difference in carotid wall thickness (intima-media thickness) in 42 unilaterally irradiated parotid tumour patients by performing B-mode ultrasonography. A mean difference in intima-media thickness (IMT) of the irradiated compared with the non-irradiated carotid artery of 0.30 mm (P=0.031) was found. A significant correlation was established with a longer post-RT interval (P=0.008). RT on the neck is associated with increased thickening of carotid IMT. Screening and treatment of additional cerebrovascular risk factors which contribute to further IMT thickening and stroke development is recommended, especially in radiotherapy patients with a favourable prognosis.