In the summer of 2011, a critically ill patient was admitted to the Neurology Intensive Care Unit (NICU): a 22-year-old female patient with progressively worsening psychobehavioral abnormalities, seizures, and impaired consciousness over the past month, with a clinical diagnosis of viral encephalitis, which continued to deteriorate despite antiviral therapy. This is when a rare “new disease”, anti-NMDA receptor antibody encephalitis, enters the differential diagnosis of a competent physician. The NMDA receptor is an ionotropic glutamate receptor that can be activated by the synthetic amino acid N-methyl-D-aspartate (NMDA). are cation channels in the postsynaptic membrane, distributed in the hippocampus and prefrontal cortex, and are closely associated with learning, memory and mental behavior. Clinical symptoms of anti-NMDA receptor encephalitis include flu-like symptoms (fever, headache, fatigue), accompanied by severe psychobehavioral abnormalities such as delusions, confusion and hallucinations, etc. Some patients are treated as psychiatric patients, and over time, patients develop symptoms such as confusion, seizures, movement disorders, and in severe cases, coma, persistent epilepsy, and hypoventilation. Most patients have unremarkable head MRI changes, but electroencephalography (EEG) often suggests widespread abnormalities and mild lymphocytic inflammation of the cerebrospinal fluid. Anti-NMDA receptors are one of the specific markers of autoimmune encephalitis and can be detected by indirect immunofluorescence, immunohistochemistry or recombinant methods to detect autoantibodies against NR1 subunit extracellular sites in the patient’s serum and cerebrospinal fluid. The diagnosis of anti-NMDA receptor encephalitis is based on specific clinical signs, MRI of the head, EEG with significant changes in CSF, and detection of anti-glutamate receptor antibodies in serum and cerebrospinal fluid. It should also be differentiated from viral encephalitis or other autoimmune encephalitis (e.g., limbic encephalitis), which has been previously reported in young women with teratomas, but cases have also been reported in women without teratomas, men, and children. If the patient is antibody positive, a full teratoma workup should be performed. In this case, ultrasonography and gynecologic consultation did reveal a pelvic mass and a high suspicion of ovarian teratoma. The patient’s blood and cerebrospinal fluid were tested for anti-NMDA receptor antibodies by the neurology pathology laboratory and the results were positive. After surgical removal of the teratoma (pathologically confirmed) and intravenous gammaglobulin treatment, the patient gradually improved and was discharged from the hospital. This was the first case of anti-NMDA receptor encephalitis diagnosed in our hospital, and the successful treatment by multidisciplinary cooperation was also recognized by the First Prize of Medical Achievement of Peking Union Medical College Hospital.