The purpose of this study is to determine the efficacy (how well the drug works), safety, and any side effects of olanzapine compared to placebo in the treatment of mania in bipolar disorder in adolescents. Both the potential benefits and side effects of olanzapine will be evaluated throughout this trial.

Inclusion Criteria:

• Male or female patients, 13 to 17 years of age who must not yet have reached their 18th birthday prior to Visit 1, when informed consent is obtained.
• Patients must have a diagnosis of bipolar I disorder and currently display an acute mania or mixed episode.
• Both the patient and the patient's parent/authorized legal representative must understand the nature of the study and must sign a document granting consent.
• Female patients of child-bearing potential must test negative for pregnancy at the time of enrollment based on a serum pregnancy test.

Exclusion Criteria:

• Female patients who are either pregnant or nursing.
• Current diagnosis of schizophrenia, schizophreniform disorder, or schizoaffective disorder.
• Patient with acute or unstable medical conditions, such that intensive care unit hospitalization for the disease is anticipated within 6 months.
• Patients who have previously not responded to an adequate dose and/or duration of olanzapine treatment.
• Patients who have been judged clinically to be serious suicidal risks.