Efficacy & Safety of Seroquel Plus Mood Stabilizer in the Maintenance of Bipolar I Disorder

Inclusion Criteria: * A diagnosis of Bipolar I Disorder, Most recent episode Manic (296.4x), or Bipolar I Disorder, Most Recent Episode Depressed (296.5x), or Bipolar I Disorder, Most recent Episode Mixed (296.6x), with or without psychotic features, as defined by Diagnostic and Statistical Manual of Mental Disorders - Fourth Edition (DSM-IV) * At least 1 manic, depressed, or mixed episode in the 2 years prior to the index episode. * Able to understand and comply with the requirements of the study. Exclusion Criteria: * Diagnosis of an anxiety disorder as defined by DSM-IV, which was treated with medication within the past year. * Known intolerance or lack of response to quetiapine fumarate or to the assigned mood stabilizer, as judged by the investigator. * Previously randomized into this study or D1447C00126