The encephalitis due to antibodies against the N-methylD-aspartate receptor is a process immune-mediated in which antibodies are directed against the GluN1 subunit of the glutamate receptor in the central nervous system. It is characterized by an acute or subacute onset of psychiatric symptoms such as confusion, short-term memory loss, behavioral changes, catatonia followed by neurological manifestations such as seizures, movement disturbances, autonomic dysfunctions, coma, and respiratory depression. It is serious and life threatening. Its association with ovarian teratoma as a paraneoplastic syndrome was described in young women. In the pediatric population it is much less frequent and is reported in publications of one or two patients and in series of few cases. We present a 13-year-old patient with encephalitis paraneoplastic due to antibodies against the N-methyl-Daspartate receptor, secondary to a mature ovarian teratoma