This is a randomized, double-blind, double-dummy multicenter study with 3 parallel arms (risperidone long-acting injectable (LAI), placebo, and olanzapine) to evaluate the efficacy and safety of risperidone LAI versus placebo in the prevention of a mood episode (recurrence event). The primary objective of this study is to evaluate the efficacy of risperidone LAI monotherapy versus placebo in the prevention of a mood episode (recurrence event) in patients with bipolar I disorder after a 12-week (3 month) stabilization period on risperidone LAI, as measured by the time to recurrence of any mood episode. This study includes 3 periods - the screening period (Period I, lasting up to 2 weeks); the open-label treatment period (Period II, lasting 12 weeks); and the double-blind treatment period (Period III, lasting up to 18 months and at least 9 months). In the open -label treatment period (Period II) treatment with risperidone LAI will be started with injection of a recommended dose of 25 mg every 14 days in patients entering Period II. If judged clinically appropriate, patients may start with 37.5 mg every 14 days. Dosage can only be increased (up to a maximum dose of 50 mg every 14 days) if the Clinical Global Impression - Severity (CGI-S) score has increased by =\> 1 over 2 consecutive assessments at least 2 weeks apart and if there is symptom exacerbation that cannot be treated adequately with short-term (14 days) benzodiazepine medication. If an increase in risperidone LAI dosage is necessary, oral risperidone (1 to 2 mg/day) needs to be added for 3 weeks after the first injection of the higher dosage. Washout of all psychotropics other than risperidone long acting must be completed by the end of the first week. Non-acute patients on an antipsychotic or mood stabilizer for at least 4 weeks will continue their previous treatment for the first 3 weeks. No changes will be made in the regimens of non-acute patients receiving an antipsychotic or mood stabilizer unless there is concern about efficacy or safety.Patients experiencing an acute manic or mixed episode will additionally be treated with oral risperidone at whole-milligram dosages between 1 and 6 mg/day as needed to treat the symptoms of the acute episode for the first 3 weeks, in order to cover the 3 weeks lag period of Risperidone long acting. Patients experiencing an acute episode who do not respond to treatment within 4 weeks will be discontinued from the study. Patients who do not show a response (acute patients at baseline) or do not maintain the efficacy (non-acute patients at baseline and acute patients after initial response) during the 12-week (3 month) open-label risperidone LAI stabilization period (Period II), will be discontinued from the study as soon as any one of the following criteria is met: The patient meets Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, text revised (DSM-IV-TR) criteria for a hypomanic, manic, mixed, or depressive episode; the patient needs treatment intervention with any mood stabilizer, antipsychotic medication (other than study drug), benzodiazepine (beyond the dosage allowed), or antidepressant medication; the patient requires hospitalization for any bipolar mood episode; the patient either has a Young Mania Rating Scale (YMRS) score \>12 in combination with CGI-S score =\>4 or a Montgomery-Åsberg Depression Rating Scale (MADRS) score \>12 in combination with a CGI-S score =\>4. (If either of these criteria is fulfilled at an assessment but if the investigator assumes that this is only a temporary state that requires no action, the investigator is allowed to postpone the decision about maintenance or response by a maximum of 4 days. If after 4 days, the criteria are still met, the patient must be withdrawn from Period II.) Patients who show initial and maintained response (acute patients at baseline) or who maintain the efficacy (non-acute patients at baseline) during the 12-week (3-month) open-label risperidone LAI stabilization period (Period II), will be eligible for entering the double-blind treatment period (Period III). Patients who enter Period III will be randomized to receive intramuscular injections of risperidone LAI every 14 days (at the dosage achieved at the end of Period II) and oral placebo daily, or placebo injections every 14 days and oral placebo daily, or placebo injections every 14 days and oral olanzapine 10 mg/day. No supplementation with oral risperidone and no dosage titration will be allowed during this period of the study. Using the double-dummy design, all patients will receive an intramuscular injection every 14 days and will take oral medication every day. Patients who present with a recurrence during Period III, will be considered as meeting the end point of the study. Patients will remain in the double-blind treatment period until they meet recurrence criteria, until they withdraw consent, or are lost to follow-up, until the last patient completed at least 9 months without a mood episode in Period III, or until the study ends. The study will end when 158 patients have presented with a mood episode in Period III, or if the study is terminated based on the decision of the sponsor. Approximately 860 patients meeting the inclusion and exclusion criteria will be enrolled in this study, with the goal of observing at least 158 recurrence events in Period III. Safety evaluations will include adverse events, clinical laboratory tests - including blood glucose/lipid profile (fasting), prolactin, TSH, and urinalysis - vital signs (pulse and blood pressure) and ECG, physical examination, body weight and height, the Extrapyramidal Symptom Rating Scale, pregnancy testing, and urine drug screen. The patients will receive risperidone LAI (25, 37.5 or 50 mg (period II)) every 14 days during the 12 week long open-label period (Period II). Patients who enter the double-blind period (Period III) will be randomized to receive intramuscular injections of risperidone LAI every 14 days and oral placebo daily, or placebo injections every 14 days and oral placebo daily, or placebo injections every 14 days and oral olanzapine 10 mg/day.