Recently, paraneoplastic encephalitis associated with ovarian teratoma,which predomi nantly affects young women,has been reported. Its symptoms are severe but often treatmentresponsive and reversible. Various psychiatric symptoms occurring shortly after onset are characteristic of this encephalitis. A 22-year-old female who had a fever and common cold-like symptoms presented with short-term memory loss. She was suspected to have viral encephalitis,but the cerebrospinal fluid（CSF）showed no marked change. Shortly after that, she developed delusions and hallucinations and presented with psychomotor excitement. She was suspected of having schizophrenia and admitted to the psychiatry department. However, several days after admission,she showed upper limb convulsion,orofacial dyskinesias,and central hypoventilation and became unresponsive. The results of laboratory tests were within the normal range, and there was no marked elevation of anti-viral antibody titers. Brain imaging was normal, but a solid tumor containing soft tissue and calcified components, probably an ovarian teratoma,was discovered on an abdominal CT scan. Anti-N-methyl-D-aspartate（NMDA）receptor antibody was positive in her CSF and blood serum,and we diagnosed her with“Anti-NMDA receptor encephalitis”. Gamma globulin was very effective,and the ovarian teratoma was removed. Finally, she could be discharged from our hospital without any sequela, and returned to her job. Psychiatrists often encounter encephalitis patients with psychiatric symptoms. If the type of encephalitis is unknown, we should keep this disease in mind.