Neuromyelitis optica (NMO) is an inflammatory demyelinating disorder characterized by optic neuritis and acute myelitis. A parainfectious pathogenesis may play a partial role in the development of this disorder. Several viral infections are known to cause NMO. Here we report the case of a 15-year-old girl diagnosed with postinfluenza monophasic NMO. The patient developed sudden fever and chills, and the rapid diagnostic test for influenza was positive. She was diagnosed as influenza A and was treated with zanamivir hydrate (10 mg/day, inhalation). Three days later, she complained of dysuria and dysesthesia in the lower extremities. After nine days, she experienced blurred vision bilaterally. Neurological examination revealed visual disturbance, dysuria, dysesthesia and hyperreflexia in the lower extremities. Her visual acuity was counting fingers in OD and 2/100 in OS. Pupillary size was 4.0 mm and light reflexes were sluggish on both sides. Ophthalmoscopy showed marked edema of the optic discs. Serum influenza immunoglobulin M antibodies were elevated and serum anti-aquaporin 4 (AQP4) antibodies were undetectable. Spinal cord magnetic resonance imaging (MRI) displayed longitudinally extensive lesions in the thoracic cord. Brain MRI disclosed three subcortical lesions. The patient fulfilled the revised diagnostic criteria for NMO (2006). After methylprednisolone pulse therapy followed by oral administration of prednisolone, visual dysfunction, dysuria, limb dysesthesia and hyperreflexia were improved. Subsequently, she experienced no attacks for 3 years. This is the first case report of influenza A-associated NMO with such features of postinfectious NMO as a pediatric onset, monophasic course and anti-AQP4 antibody-seronegative status.