Anti-NMDA receptor encephalitis is the most common curable non-infectious autoimmune encephalitis，but because of the lack of recognition in the clinic, usually been misdiagnosed as other causes of encephalitis. Therefore, it is urgent to establish a database of anti-NMDA receptor encephalitis in Chinese population. The multi-center, prospective clinical trial of anti-NMDA receptor encephalitis in China's , combined with Beijing Xuanwu hospital, Beijing Tiantan Hospital, Beijing Children's Hospital and other hospitals around the country, by screening the NMDA receptor antibody and summarizing the cases analysis, in order to provide evidence for clinical diagnosis and treatment of anti-NMDA receptor encephalitis.

Inclusion Criteria:

1. Older than 6 months.
2. Encephalopathy symptoms (change of mental state and consciousness level) persist for more than 24 hours;
3. At least one or more clinical features of the followings: fever, epilepsy, focal neurological deficiency symptoms, changes in CSF(cerebrospinal fluid inflammatory), changes in EEG (electroencephalogram), radiographic abnormalities;
4. Clinical suspected encephalitis, but conventional detected methods cannot make etiology clear.
5. Signed informed consent

Exclusion Criteria:

1. Infants less than 6 months;
2. The metabolic encephalopathy;
3. Infectious encephalitis with clear pathogen clinically, referring the specific pathogenic microorganisms, including: bacteria, virus, fungus, parasite, spirochete and so on;
4. Non-infectious encephalitis with clear diagnosis clinically, including: multiple sclerosis, neuromyelitis optic, acute disseminated encephalomyelitis and so on.

the unidentified encephalitis patients who meeting the inclusion criteria and exclusion criteria and signing the written informed consent form。