This study aims to evaluate the safety and efficacy of risperidone as an adjunctive therapy to mood stabilizers in the long-term treatment (6months) of bipolar disorder using various assessment instruments, including the Young Mania Rating Scale. The Simpson-Angus Rating Scale will be also employed to assess the presence of extrapyramidal side effects and other adverse events. The patients will receive orally 0.5, 1, 2 mg risperidone tablet once daily for 6 months