Pathophysiological investigations concerning malignant neuroleptic syndrome (MNS), reveal lower levels of the Dopamine, caused by D2 receptors blockade in the hypothalamus and nigrostriar system or disfunction of the dopamine receptors. The blocking conductance in the hypothalamus provides thermo disregulation and peripheral effects of the neuroleptics – to liberation of Ca 2+ from the endoplasmatic reticulum. The aim of this study was to research and to follow up the case history in 18-year-old schizophrenic male patient. The case history describes the typical clinical symptoms and the biochemical constelations, compatible with MNS. Materials and methods: The patient was admitted from emergency department of the University Hospital – Pleven in intensive care department. He was in severe condition. He was stopping the mono neuroleptic therapy for 3 weeks. After the iniciation of the treatment with low doses, he developed MNS.The patient was checked by psychiatrist, exact internal clinical examination, neurological examination, biochemistry tests, CT of the brain, reanimation procedures and treatment by anesthesiologist and neurologist. Rezults and analyze: The analyze of the received results reveals benign prognosis, if the treatment starts to admit of no delay. For this patient, even small doses from the neuroleptic drug can produce severe health changes. The effects of this medication are not depending on the dose. Individual predispozition must keep in mind. The differential diagnose is difficult, because the symptoms of the MNS and of the serotonin syndrome (SS), and some other clinical manifestations can be impossible to differentiate.