The objective of this study is to demonstrate that there is a benefit in switching chronic schizophrenic patients from conventional antipsychotic to olanzapine in terms of efficacy, neurological safety and patient's outcome.

Inclusion Criteria:

Schizophrenic patient meeting the DSM-IV diagnostic criteria more than one year ago and treated with antipsychotic for at least 1 year.

Outpatient (or patient admitted to hospital for social or logistic reasons).

Patient receiving a stable dose of the same conventional antipsychotic for at least 8 weeks before visit 1.

Patient presenting a PANSS score equal or greater than 49 at Visit 2.

Patient considered by the investigator as possible candidates for a switch, owing to inadequate efficacy or poor safety of the current treatment.

Exclusion Criteria:

Patient presenting a schizophreniform or a schizo-affective disorder according to the DSM-IV diagnostic criteria, or any other disorder from Axis I of the DSM-IV, or a disorder from Axis II (limit personality), substance dependence or substance abuse.

Administration of an atypical antipsychotic drug during the 8 weeks preceding V1.

History of resistance to antipsychotic drugs

Hospitalization in a psychiatric unit or in a psychiatric emergency department within the 8 weeks preceding the beginning of the study.

Presence of serious unstable disease, such as a fatal outcome or hospitalization in an intensive care unit, is foreseeable within a period of 6 months.