Anti-N-methyl-d-aspartate (NMDA) receptor encephalitis is a life-threatening disorder that often occurs as a paraneoplastic encephalitis and usually begins with neuropsychological or psychiatric symptoms. We report a case of NMDA receptor encephalitis due to an ovarian teratoma, which began with severe and progressive amnesia and behavioral changes, reversed after surgical treatment and plasmapheresis. Using a battery of cognitive tests, its neuropsychological profile before treatment showed a complete alteration of the short and long term memory of both verbal and visual fixation, with clear improvement with cues and with intrusions, and saving other cognitive domains, such as working, episodic and semantic memory, executive, visuospatial, praxical thinking and language functions. These deficits reverted to normalcy with treatment. So, we can conclude that anti-NMDA receptor encephalitis is a rare entity that can be potentially serious depending on early management and diagnosis. We must suspect this entity in children or young people presenting with behavioural disturbances and crisis, with a cognitive pattern of complete alteration in short and long term memory improving with cues, and respecting other cognitive domains.