The primary aims of this study were (i) a replication of the effectiveness and tolerability of risperidone in the treatment of patients with acute mania in a very large cohort in a naturalistic treatment setting and (ii) to extend the data on the effect and tolerability of risperidone in the treatment of patients with acute mania to an Asian population. A total of 909 patients fulfilling DSM-IV criteria of bipolar disorder (current manic and hypomanic episode) entered this large, open, multicentre study. The Young Mania Rating Scale (YMRS), Clinical Global Impression (CGI) and Simpson-Angus Rating Scale (SARS) were measured at baseline and weeks 1, 3 and 6, for the assessment of effectiveness and extrapyramidal symptoms. This study showed a statistically significant reduction of scores on the YMRS and CGI-severity (mean change=-23.5+/-11.8, P<0.0001; mean change=-2.7+/-1.5, P<0.0001, respectively) from baseline to endpoint (week 6). The number of patients with a 50% reduction or more in the YMRS and CGI-severity scores was 693 (77.8%) and 630 (70.7%) at endpoint, respectively. There were no statistically significant increments of scores on SARS. Risperidone was generally well tolerated. The present larger open study indicates that risperidone add-on therapy is effective and tolerable in treatment of bipolar disorder, replicating results in various controlled and uncontrolled studies from Western countries.