Background: Recurrent optic neuritis (ON) was previously thought to be associated with multiple sclerosis (MS) and neuromyelitis optica spectrum disorders (NMOSD). Meningoencephalitis has recently been suggested to be a clinical finding typical of myelin oligodendrocyte glycoprotein (MOG) encephalomyelitis. We report a Chinese patient with recurrent ON at disease initiation, who had a delayed diagnosis of MOG-IgG syndrome, until recurrent meningoencephalitis appeared and serum MOG-IgG was detected. Case presentation: From the age of 7 years, an AQP4-IgG negative female patient had 10 disease recurrences, including 4 episodes of recurrent ON, 4 episodes of fever and meningoencephalitis, and 2 episodes of ON as well as meningoencephalitis. She was initially diagnosed as recurrent ON and treated with glucocorticoids followed by gradual tapering when ON reoccurred. Later, she was diagnosed as central nervous system infection when fever and meningoencephalitis appeared, and antiviral drugs and glucocorticoids were used. However, when she returned to our department for follow-up on July 2017, the results of serum demyelinating autoimmune antibody revealed positive MOG-IgG (titer 1:320 by an in-house, cell-based assay using live cells transfected with full-length human MOG). A diagnosis of MOG-IgG syndrome was established. Conclusions: Testing for MOG-IgG in atypical MS and NMOSD patients, and patients with meningoencephalitis with a history of relapsing demyelinating symptoms is warranted.