Optic neuritis is clinically suspected when painful, rapidly progressive central visual loss occurs in a young patient who has a relative afferent pupillary defect. Ophthalmoscopy is normal in the majority of cases but papillitis or optic disc palor can occur. Several other diseases can mimic optic neuritis, such as ophthalmological conditions or other diseases affecting the visual pathways. Their appropriate clinical diagnosis is of paramount importance in order to avoid unnecessary or invasive procedures or treatments.