Chickenpox may lead to several neurologic complications, but optic neuritis has rarely been described. We report on a 6-year-old immunocompetent patient who presented with unilateral optic neuritis and severe visual loss because of varicella infection. A week after varicella eruption, the child experienced blurred vision. An examination revealed decreased visual acuity of his right eye, a right pupil poorly reactive to light, and almost no color vision in his right eye. A history of chickenpox, the fundus examination, and the measurement of visual-evoked potentials allowed us to make a diagnosis of optic neuritis caused by varicella infection. The patient received only symptomatic relief with antipyretics. Three months later, his visual acuity improved to 20/40 in the right eye.