RISPERDAL CONSTA (risperidone long-acting injection) may provide substantial improvement, by reducing patient non-compliance, in the long-term treatment of bipolar I disorder. This is a randomized (patients are assigned different treatments based on chance), double-blind, (neither the patient nor the physician knows whether drug or placebo is being taken, or at what dosage) placebo-controlled study to explore the safety and effectiveness of RISPERDAL CONSTA in the prevention of mood episodes in patients with bipolar 1 disorder. This study includes 5 periods: a screening period lasting up to 1 week; an open-label RISPERDAL (oral risperidone) treatment period lasting 3 weeks; an open-label RISPERDAL CONSTA stabilization period lasting 26 weeks; a double-blind period lasting up to 24 months; and an open-label extension with RISPERDAL CONSTA lasting 8 weeks. Efficacy will be assessed using the Young Mania Rating Scale (YMRS), Montgomery-Åsberg Depression Rating Scale (MADRS), Clinical Global Impressions - Severity (CGI-S) scale, Medical Outcomes Study Short Form 36 (SF-36), and the Personal and Social Performance (PSP) scale. Safety will be evaluated throughout the study and includes assessment of adverse events, clinical laboratory tests (including hematology, serum chemistry, blood glucose/lipid profile, prolactin, and urinalysis); electrocardiograms (ECGs), vital signs (pulse and blood pressure), physical examination, body mass index (BMI), and the Extrapyramidal Symptom Rating Scale (ESRS). Oral risperidone (flexible dosage) 1 to 6 mg/day for the first 3 weeks. Risperidone LAI i.m. injections (12.5mg, 25 mg, 37.5 mg, or 50 mg) given every 2 weeks for up to approximately 2.6 years (only 6 months for patients receiving placebo during DB-period)