• The change in the total YMRS score from baseline at the 3-week endpoint
  

• Effects on secondary efficacy variables (YMRS response and onset of maintained response, Clinical Global Impression Scale - Bipolar Disorder [CGI-BP]), safety, tolerability, and pharmacokinetics.
  

Subjects will be aged 10 to 17 years with a diagnosis of Bipolar I disorder and suffering from a current mixed or manic episode. On enrollment, subjects will be assigned to receive 1 of 3 treatments (oral placebo tablets, oral risperidone tablets 0.5 to 2.5 mg, or oral risperidone tablets 3 to 6 mg), which will be administered daily for 3 weeks. Study medication will be increased to the target dosage during the first 7 days, then further increased within the target dosage range reached until maximum tolerated dose is reached by day 10. The maximum tolerated dose will be given for the last 12 days of the study.

Risperidone (0.5 to 2.5 mg or 3 to 6 mg doses) or placebo given orally as 0.25, 0.5, 1, 2, 3, or 4 mg tablets (or matching placebo) each day for 3 weeks.

Inclusion Criteria:

• Current primary diagnosis of bipolar I disorder, mania or mixed type
• Aged between 10 and 17 years
• Young Mania Rating Scale score greater than or equal to 20 at screening and baseline

Exclusion Criteria:

• Known or suspected history of substance dependence
• Significant risk for suicidal or violent behavior
• Received electroconvulsive treatment within 4 weeks of baseline
• Received a depot antipsychotic within 2 treatment cycle before baseline
• Is unable to swallow medication taken in the form of tablets
• Has a positive result for a urine drug screen done at baseline
• Known or suspected seizure disorder
• Hypothyroidism or hyperthyroidism, unless stabilized on appropriate medication for at least 3 months before screening
• Known or suspected history of hypersensitivity or intolerance to risperidone
• History of a poor antimanic response to risperidone when used in adequate doses for an adequate period as the sole antimanic agent