"Acute non-herpetic encephalitis" was consisted of several non-herpetic encephalitides including "acute juvenile female non-herpetic encephalitis (AJFNHE)" and "non-herpetic limbic encephalitis(NHLE)". In 1997, we first reported five young adult female patients with acute non-herpetic encephalitis who presented with severe prolonged coma and status epilepticus, but achieved a good recovery. Following this report, the results of a clinical analysis on 89 serial patients with encephalitides indicated that such patients presented specific and different clinical features, including the frequent detection of anti-glutamate receptor (GluR) antibody as compared with other etiologies of encephalitis. Since all of their 11 patients were young adult women, we designated these patients as "acute juvenile female non-herpetic encephalitis (AJFNHE)". In 2007, Dalmau et al. reported anti-N-methyl-D-aspartate receptor(NMDAR) encephalitis associated with ovarian teratoma. We recently reported the results of a nationwide survey on AJFNHE in Japan. This result was indicated that AJFNHE and anti-NMDAR encephalitis were inferred to be almost identical condition. AJFNHE thus represented a clinical concept based on the specific clinical features, and anti-NMDAR encephalitis represented a clinical entity based on the neuro-oncological findings including the NMDAR NR1 and NR2 heteromer antibody.