To evaluate the efficacy of quetiapine versus placebo in increasing time from randomization to recurrence of a mood event in patients with Bipolar I Disorder. Recurrence of a mood event is defined as fulfilling at least 1 of the following: (a) initiation of an antipsychotic, antidepressant, mood stabilizer, anxiolytic other than lorazepam, or any other medication to treat a manic, depressed or mixed event, (b) hospitalization for a manic, depressed or mixed event, (c) Young Mania Rating Scale (YMRS) score more than or equal to 20 at 2 consecutive assessments or at the final assessment if the patient discontinues, or Montgomery-Asberg Depression Rating Scale (MADRS) score more than or equal to 20 at 2 consecutive assessments or at the final assessment if the patient discontinues, or (d) discontinuation from the study by the patient if, in the opinion of the investigator, the discontinuation was due to a manic, depressed or mixed event.