Devic's neuromyelitis optica (NMO) onset is characterized by optic neuritis (ON) and transverse myelitis (TM), either simultaneously or in isolation. Thereafter, the course of the disease can be monophasic (no other attack) or relapsing (sequences of ON and TM, no other neurological system involved). The risk of having a relapsing course is related to gender, older age at onset, less severe motor impairment after the myelitic onset, interval length between first and second attack. The risk of an unfavourable evolution (severe disability or death) during a relapsing course is mainly related to high relapse rate during the first two years of the disease. In summary, relapsing NMO patients tend to have a poor prognosis, requiring more effective immunosuppressive treatments.