Neuromyelitis optica (NMO) has been attributed to different underlying pathological events. The aim of this paper is to present the first case report of a patient with Down's syndrome (DS) who died of a fulminant NMO. A 29-year-old woman with DS developed acute transverse myelitis, with complete visual loss and swollen optic discs. Two days later, she developed quadriplegia, respiratory arrest and died. The anatomical study demonstrated typical findings of DS in the brain without demyelinating lesions. A severe destruction of medulla and cervical cord with a very high degree of demyelination of the optic nerves was typical of monophasic NMO (Devic's disease). Most of the cases of NMO in Cuba are of the relapsing form, but this case report is the first one with monophasic NMO and DS with a very aggressive course. The link of the pathogenetic relationship between DS and NMO remains unclear; it may well be coincidence but the fact that the patient died very shortly after the onset suggests, at least on clinical grounds, that the presence of DS could have accelerated the fatal evolution of NMO.