Some Inclusion Criteria:

• Patients must have a diagnosis of Schizophrenia as defined in Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) (Disorganized, 295.10; Catatonic, 295.20; Paranoid, 295.30; Residual, 295.60; or Undifferentiated, 295.90) and confirmed by the Structured Clinical Interview for DSM-IV (SCID).
• Patients must meet the following psychopathologic severity criteria at Visit 1: Brief Psychiatric Rating Scale (BPRS) total score, extracted from the Positive and Negative Syndrome Scale (PANSS), of at least 45 (18-item version, in which 1 indicates "absent" and 7 indicates "severe"). In addition, item scores of at least 4 (moderate) will be required on 2 of the following BPRS items: conceptual disorganization, suspiciousness, hallucinatory behavior, and/or unusual thought content.
• Patients must receive a rating of 4 (moderately ill) or greater on the Clinical Global Impression-Severity (CGI-S) scale at Visit 1.
• Patients in whom, in the opinion of the investigator, a switch to another antipsychotic medication or initiation of an antipsychotic medication is acutely indicated.

Some Exclusion Criteria:

• Patients in whom treatment with olanzapine or placebo is relatively or absolutely clinically contraindicated.
• Patients who have a history of inadequate response to an adequate treatment trial with olanzapine, in the opinion of the investigator.
• Patients who have received treatment with olanzapine within 6 weeks prior to Visit 1.
• Patients who have received treatment with clozapine at doses greater than 200 mg daily within 12 months prior to Visit 1, or who have received any clozapine at all during the month before Visit 1.
• Patients who have a history of an inadequate response, in the opinion of the investigator, to 2 or more adequate antipsychotic medication trials of at least 8 weeks duration in the past 12 months prior to Visit 1.
• Patients with acute, serious, or unstable medical conditions, including (but not limited to) inadequately controlled diabetes (hemoglobin A1c (HbA1c) 8%), severe hypertriglyceridemia (fasting triglycerides 5.6 mmol/L, recent cerebrovascular accidents, serious acute systemic infection or immunologic disease, unstable cardiovascular disorders (including ischemic heart disease), malnutrition, hepatic, renal, gastroenterologic, respiratory, endocrinologic, neurologic, or hematologic diseases.