To assess the 5-year visual course, including the incidence of recurrent optic neuritis, in 454 patients enrolled in the Optic Neuritis Treatment Trial.Five-year follow-up vision testing, which included measures of visual acuity, contrast sensitivity, visual field, and color vision, was completed for 397 (87%) of the 454 patients.Visual function test results in the eyes that experienced optic neuritis at study enrollment (affected eyes) were normal or only slightly abnormal after 5 years in most patients; the results did not significantly differ by treatment group (P=.37 for visual acuity). The visual acuity in the affected eyes was 20/25 or better in 87%, 20/25 to 20/40 in 7%, 20/50 to 20/190 in 3%, and 20/200 or worse in 3%. The recurrence of optic neuritis in either eye occurred in 28% of the patients and was more frequent in patients with multiple sclerosis (P=.001) and in patients without multiple sclerosis who were in the prednisone treatment group (P=.004). Most eyes with a recurrence retained normal or almost normal visual function.Most patients retained good to excellent vision in the 5 years following an attack of optic neuritis, even if the optic neuritis recurred. Recurrences were more frequent in patients with multiple sclerosis and in those treated with oral prednisone alone. The completion of the 5-year follow-up by the Optic Neuritis Treatment Trial cohort has not altered our management recommendations based on the results we reported earlier.