The purpose of the study is to investigate the action of one antipsychotic molecule of recent introduction on the market. Paliperidone, in this occasion used in the formulation extended-release tablets, is an oral antipsychotic who takes advantage of the OROS system. Studies about are up to now focused on the effectiveness of paliperidone ER in the acute phase of the schizophrenia. In our job we have, instead, intention to show one possible application in a case of a chronic patient with undifferentiated schizophrenia resistant to the other antipsychotic treatments. Moreover 3TRE scale has been associated to establish the effects of the new therapy. The entrance prescription has been with paliperidone ER in a dosage of 6mg once a day. Clinical effects of paliperidone ER 6 mg became obvious and meaningful, online with other jobs, already in the first days of treatment. But the improvement of the partials and totals scale's scores have been had mainly with the dosage to 12 mg, that the patient has assumed autonomously unknown to the care provider.