A 2-year and 7-month-old boy had sudden visual loss in both eyes and showed bilateral optic neuritis without systemic symptoms. Steroid therapy improved his visual acuity from 0.077 and 0.053 to 1.0 at 7 months after onset. Magnetic resonance imaging (MRI) of the brain showed high density in both optic nerves and multiple lesions in the white matter that were enhanced by gadolinium. We considered the diagnosis of demyelinating disease. Follow-up MRI showed no abnormal lesion. Both transient and steady-state pattern visually evoked cortical potentials were nondetectable at the onset, and the P100 component of the transient pattern reversed visually evoked cortical potential appeared to be delayed thereafter. It has since become shorter in parallel with visual acuity improvement.