A 15-year-old girl presented with a headache accompanied by bilateral visual impairment. Brain magnetic resonance imaging showed tumefactive lesions in the white matter of the right occipital lobe on fluid-attenuated inversion recovery images accompanied by open-ring gadolinium enhancement and high-intensity lesions in the bilateral optic nerve, including chiasma. Since anti-myelin oligodendrocyte glycoprotein (MOG) antibody was detected by blood examination, the patient was diagnosed with anti-MOG antibody-associated disease (MOGAD) exhibiting overlapping characteristics with tumefactive multiple sclerosis (MS) and neuromyelitis optica spectrum disorders (NMOSD). Steroid pulse therapy and plasma exchange therapy completely improved her symptoms, and oral prednisolone therapy prevented relapse of the disease for at least 2 years. Since MOGAD exhibits overlapping characteristics with MS and NMOSD, it is important to screen anti-MOG antibodies in patients with atypical MS and seronegative NMOSD.