The inflammation of the optic nerve called optic neuropathy could be an onset marker of multiple sclerosis. The authors review the place of optic neuropathy (neuritis) in the inflammatory demyelinating disease continuum, especially as the onset symptom of multiple sclerosis. We present the clinical symptoms, the aetiology of optic neuritis and the adjacent methods used to investigate optic neuritis. In the article are presented the actual criteria used to establish the multiple sclerosis diagnosis and the revised criteria for optic neuromyelitis, with emphasis on the differential diagnosis between these diseases.