The purpose of this randomized, double blind, double dummy, multicenter study was to evaluate the efficacy of risperidone long-acting injectable (LAI) monotherapy in comparison with placebo in the prevention of a mood episode in treatment of patients with bipolar I disorder. Oral olanzapine was used to assess the validity of the study design. The primary objective of this study is to evaluate the efficacy of risperidone LAI 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. Risperidone LAI has been approved by the FDA in the USA for the treatment of patients with schizophrenia and for the prevention of mood recurrences in bipolar I disorder, as monotherapy or add-on treatment. It is approved at EMEA and other European and non-European health authorities for the treatment of patients with schizophrenia, too.