Carotid artery vasculopathy is a long-term complication of radiotherapy (RT) of the neck. We investigated the change in carotid intima media thickness (IMT) and the incidence of ischemic stroke in the first 7years after radiotherapy (RT) of the neck.A multicentre prospective cohort study among patients treated for Head and Neck Cancer (HNC) assessed carotid IMT at baseline (before RT) and after a median of 7years follow-up. We also screened for cerebrovascular risk factors and events.48 patients underwent IMT measurement at baseline and follow-up (median age 61years, range 29-87). Mean IMT of the irradiated common carotid arteries was 0.64mm at baseline and 0.74mm at follow-up (p=0.002). Mean delta IMT in the irradiated and non-irradiated common carotid arteries were 0.11 and 0.02mm (p=0.03). Incidence rate of stroke in our cohort, compared to the Dutch population was 8.9 versus 1.5 per 1.000 person years.IMT in irradiated carotid arteries was significantly increased in the first 7years after RT. The incidence rate of stroke was six fold increased. Patients treated with RT for HNC have sustained risk for developing atherosclerosis of the carotid arteries and future stroke.