Objective: To analyze the imaging characteristics of congenital absence of internal carotid artery. Methods: The clinical symptoms and imaging characteristics of a case of congenital absence of internal carotid artery were retrospectively analyzed. Results: The ultrasound findings showed that the left superior thyroid artery originated from the left common carotid artery, and the distal branch of the left common carotid artery did not have an internal carotid artery like lumen and blood flow spectrum entering the intracranial region. The distal branch had a high blood flow resistance index (RI) that resembled an external carotid artery like spectrum, and the left cervical vascular lumen was thinner than the contralateral side. CTA of the head and neck showed that the left internal carotid artery was not developed, and the left anterior cerebral artery was supplied by the opposite anterior cerebral artery. The A1 segment of the brain was absent. The left middle cerebral artery was supplied by the vertebrobasilar artery, and the left carotid canal was absent. The diagnosis was confirmed as congenital absence of internal carotid artery. Conclusion: Ultrasound examination is convenient, inexpensive, safe, and real-time dynamic observation. It can be used as an important means of preliminary screening, early detection, and early prevention to reduce the risk of stroke.