This exploratory analysis was performed to compare the efficacy and tolerability of risperidone when added to two different mood stabilizers (lithium or valproate) for mania in bipolar disorder. Patients receiving lithium or valproate at baseline were drawn from the database of a 12-week, open-label risperidone study. The primary efficacy measure was the Young Mania Rating Scale (YMRS). Other assessments included the Hamilton Rating Scale for Depression (HAM-D), Clinical Global Impression (CGI) of improvement, and safety measures. The analysis included 33 patients on lithium plus risperidone and 46 patients on valproate plus risperidone. Both subgroups had comparable baseline YMRS scores (lithium 28.2, valproate 28.7) and both had significant reductions in score by week 1 (P<0.0001). Comparable reductions in score continued for both subgroups until the end of the study (YMRS scores at week 12: lithium 4.6 and valproate 6.7). There were no significant differences in response rates (≥50% improvement on YMRS) or remission rates (YMRS score ≤8) between the two subgroups. At week 12, 88% of the lithium plus risperidone patients and 80% of the valproate plus risperidone patients were in remission. Similarly, HAM-D scores were significantly and comparably reduced in both subgroups, and improvement in CGI was the same. There was no difference between subgroups in the incidence of adverse events or weight gain. These data suggest that risperidone can be safely combined with either lithium or valproate, and that the efficacy is similar regardless of the mood stabilizer used.