In a recent study, administration of granulocyte colony stimulating factor (G-CSF) increased neuromyelitis optica (NMO) lesions in mice. Here we report a patient whose first episode of NMO may have been exacerbated by inadvertent administration of G-CSF. Histological examination of brain and spinal cord samples from three other NMO patients revealed markedly increased expression of G-CSF in neurons located in and around the lesions, with little or no expression in multiple sclerosis lesions or normal white matter. Taken together, these cases support a detrimental role for G-CSF in NMO pathogenesis.