Monophasic neuromyelitis optica (NMO) is a rare form of post-infection acute disseminated encephalomyelitis (ADEM). Cases occurring after dengue virus infection are rare, despite the high prevalence of this disease in tropical and subtropical countries. We report a female patient, 11 years old, of Japanese ancestry and living in North Brazil, who developed NMO 1 week after having had a benign form of dengue fever. The disease was confirmed by the detection of dengue IgM antibodies in serum and cerebrospinal fluid (CSF). Restricted distribution of the lesions in the optic nerve and spinal cord was confirmed by ophthalmological evaluation and magnetic resonance imaging of the brain and spinal cord. Therapeutic intervention with corticotherapy resulted in benign evolution. This is the second report of optic spinal syndrome following dengue virus infection in patients of Japanese ancestry, suggesting an influence of the genetic background in the susceptibility to post-dengue NMO.