The onset of multiple sclerosis after the age of 50 years is rare. We report four patients with optic neuritis and oligoclonal bands or increased IgG production in the cerebrospinal fluid. Three of them subsequently developed clinically definite multiple sclerosis. Four apparently healthy women, 62, 56, 50 and 50 years of age, presented with progressive visual loss, three patients in one eye and one patient in both eyes. The diagnostic work-up revealed no findings indicating an ischemic process, an infectious, systemic inflammatory, or neoplastic disease. Examination of the cerebrospinal fluid revealed oligoclonal bands and/or increased production of IgG. Visual acuity recovered during the following weeks to 8 months. Three of the 4 patients subsequently developed additional neurologic signs compatible with multiple sclerosis. Optic neuritis can be the presenting sign of multiple sclerosis even after the age of 50.