An autoimmune acute encephalitis caused by antibodies against the glutamate NMDA receptor. It usually affects females and in the majority of cases it is associated with the presence of a tumor, most commonly an ovarian teratoma. The presence of a tumor in patients with this form of encephalitis implies that the latter is a paraneoplastic syndrome. It is manifested with psychiatric symptoms and epileptic seizures. It is a potentially lethal disorder; however, it is usually reversible with the prompt removal of the tumor.