A psychosis in a 5 years old girl is reported. By the 2nd month of her illness there was clear mental regression, with disorders of contact, motricity, speech, instinctive behavior and pragmatism. Neurologic and electroencephalo-graphic abnormalities, together with the psychiatric symptoms, lead to the diagnostic of organic psychosis. High doses of neuroleptics were used and there was progressive remission of the symptoms, beginning at the 3rd month of disease. The etiologic diagnosis (being more probable a demyelinizing encephalitis) and the therapeutic effect of the neuroleptics are discussed.