Although associations between antipsychotic use and neuropsychological impairment in bipolar I disorder have been observed, there is a lack of studies comparing the effects of specific agents used in this population. We compared performance between patients receiving maintenance treatment with mood stabilizer monotherapy (n=15), adjunctive risperidone (n=15) or quetiapine (n=17), and a group of demographically matched healthy controls (n=28) on tests of executive function (working memory, set shifting, and inhibition) and verbal learning. Despite having a similar clinical profile, patients being treated with risperidone showed significantly impaired working memory, set-shifting, and verbal learning (P<0.05) compared with those either on mood stabilizer monotherapy or adjunctive quetiapine. Although randomized controlled trials are required to confirm the cognitive side effects of medications prescribed for maintenance treatment of bipolar I disorder, preliminary results indicate that addition of risperidone to a mood stabilizer has a negative impact on executive function and verbal learning, an effect not shared with quetiapine.