N-methyl-D-aspartate receptor (NMDAR) antibody encephalitis is a recently described immunotherapy-responsive panencephalitis with characteristic features that include a psychiatric onset and a later movement disorder. This entity was first described as a paraneoplastic phenomenon in young women with ovarian teratomata. However, more recently it has become clear that the majority of patients, particularly children, do not harbor a tumor and that males can also be affected. With the development of the NMDAR antibody assay, now available worldwide, a few patients with classical limbic encephalitis and early psychosis and epilepsy have also been found to harbor these antibodies. Early diagnosis followed by immunotherapies and tumor removal, when relevant, expedite recovery from the condition. Antibody levels correlate with the clinical severity of the disease in individual patients, and the antibodies have been shown to substantially reduce NMDA receptors on hippocampal neurons both in vitro and in vivo, supporting the likely direct pathogenicity of the NMDAR antibodies.