Devic's neuromyelitis optica (NMO) is a clinical entity characterised by severe transverse myelitis, optic neuropathy and monophasic or recurrent course. We report the case of a woman affected by myelitis and optic neuritis suggesting Devic's disease. Diagnosis was supported by clinical, neuroradiological and biochemical findings. In 14 months, the patient developed 5 clinical exacerbations. Six cerebrospinal fluid (CSF) examinations were performed, 3 during relapses and 3 during remitting phases: all the CSF specimens obtained during relapses showed granulocyte pleocytosis and increased protein level, whereas CSF was normal during stationary phases. Oligoclonal banding was always absent. Spinal cord MRI showed altered signal at cervical and thoracic levels. We did not find any concomitant systemic disease. The case we report underlines the importance of CSF examination during clinical relapse in NMO diagnosis.