We examined visual evoked potentials and pattern electroretinograms in a patient with Tolosa-Hunt syndrome associated with optic nerve involvement. The 82-year-old woman developed unilateral painful ophthalmoplegia and visual loss in the right eye. Magnetic resonance imaging showed an abnormal soft-tissue area in the right cavernous sinus and the right orbital apex. Symptoms responded rapidly to treatment with corticosteroid. Visual evoked potentials to flash and pattern stimuli were both remarkably reduced and delayed in the right eye in the acute stage; however they improved to almost normal after steroid therapy. The pattern electroretinogram recorded in the acute stage was normal bilaterally. These results indicate that optic nerve involvement in Tolosa-Hunt syndrome can be mild and reversible.