This study is being carried out to see if quetiapine (Seroquel) is effective in preventing patients from a schizophrenic relapse when studied for a long time (1 year) and if so, how it compares with non-active treatment.

Inclusion Criteria:

• Stable schizophrenic patients who have provided written informed consent
• Patients 18 to 65 years old who remain clinically stable after switching to a stable dose of Seroquel (quetiapine).

Exclusion Criteria:

• Patients with risk of suicide, other disorders or substance abuse that might interfere with the patient's ability to co-operate,
• Expected non-compliance to treatment
• Known diabetes mellitus,
• Contraindications,
• Intolerance or non-responsiveness to Seroquel or other safety issues.