A extremely rare case of unilateral retinocephalic vascular malformation (Wyburn-Mason syndrome) was reported. A 5 year-old girl was seen to a ophthalmologist complaining of exophthalmus of her left eye after trauma on her face for the past 2 months. On ophthalmologic examinations, retinal arteriovenous malformation was recognized in her left eye and she was referred to neurosurgical service for the evaluation on occurrence of traumatic carotid cavernous fistula. Plain CT did not show any abnormality but enhanced CT revealed an abnormally enhanced lesion in the thalamus and basal ganglia and along to the left optic nerve. Left carotid angiography and vertebral angiography revealed a huge arteriovenous malformation in the left thalamus and basal ganglia extending to the left orbita. The arteriovenous malformation was fed from the C3 segment of the carotid artery, anterior, middle and posterior cerebral arteries, and drained to the internal cerebral vein and basal vein. The intraorbital part of the malformation was mainly fed from the external cerebral artery. She was diagnosed as Wyburn-Mason syndrome. We stressed in the paper that enhanced CT was useful for the diagnosis of the Wyburn-Mason syndrome.