In three women aged 20, 34 and 21, with a combination of optic neuritis and transverse myelitis, the diagnosis of neuromyelitis optica (Devic's disease) was made. All three were treated with methylprednisolone. The first patient died from respiratory failure associated with tetraparesis, over two years after experiencing initial symptoms. The other two women recovered to varying extents. By employing a combination of clinical investigations and MRI supplemented by laboratory investigations, it is possible to differentiate neuromyelitis optica from multiple sclerosis. Neuromyelitis optica is treated by a stronger form of immunosuppression. Despite recorded differences it remains possible that these conditions form part of the same spectrum in which the genetic background is important. In neuromyelitis optica the underlying condition seems to be in the field of the human immune response.