To report a case of moyamoya disease initially presenting transient visual loss in a healthy young subject.

A 20-year-old male with no history of systemic disease or trauma visited our clinic due to sudden onset visual loss in the right eye. There were no accompanying symptoms, including headache, seizure, paresis, or paresthesia. Best corrected visual acuity at the first visit was hand movement in the right eye and 20/20 in the left eye. No abnormal finding was revealed in the anterior segment. On fundus examination, whitening at post pole was found in the right eye. In fluorescein angiography, a choroidal and retinal artery filling delay in the posterior pole was noted. The patient's visual acuity began to improve gradually and was recovered to 20/20 by the next day. Moyamoya disease was diagnosed based on magnetic resonance angiography of the brain and transfemoral cerebral angiography as well as stenosis of the internal carotid artery and middle cerebral artery with collateral vessel networks.

Moyamoya disease should be considered as a possible cause of transient visual loss in healthy young subjects.