Dysgenesis of THE internal carotid artery is considered a rare condition, present in about 0.01% of subjects. This anomaly is generally asymptomatic and often represents an incidental finding in radiological examinations of the head performed for other reasons. A 75-year-old woman with symptoms of dementia was admitted to our hospital. Computed tomography and magnetic resonance examinations were performed. They showed the absence of both internal carotid arteries and the congenital nature of this abnormality. The usefulness of CT and MRI examinations in patients with this vascular abnormality is discussed.