To accommodate for the latency period (i.e., the time for risperidone to be released from the microspheres and approach therapeutic plasma levels), subjects entering into the study will continue on oral risperidone for the first three weeks (Days 0-21). Temporary oral supplementation will also be permitted anytime during the stabilization phase of the study when considered by the treating physician to be clinically necessary for the treatment of breakthrough psychosis. With only one exception, the treating physician is not restricted from adding or discontinuing any pharmacological treatment deemed necessary for the clinical management of the subject. The exception in this case prohibits the addition of another antipsychotic agent and applies only to the stabilization phase of the study.