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Objectives:We use an emotional saccade task to characterize executive functioning and emotion processing in adult Attention-deficit hyperactivity disorder (ADHD) and bipolar disorder (BD).Background:ADHD and BD share cognitive and emotion processing deficits that complicate differential diagnoses. Our ability to distinguish the symptomology of ADHD and BD, as well as to understand their underlying mechanisms, is limited by a lack of valid behavioral markers that support the diagnosis.Materials and Methods:Participants (21 control, 20 ADHD, 20 BD) performed an interleaved pro/antisaccade task (look toward vs. look away from a visual target, respectively) in which the sex of emotional face stimuli acted as the instructional cue to perform either the pro- or antisaccade.Results and Conclusions:Both patient groups made more direction errors (erroneous prosaccades on antisaccade trials) and anticipatory errors (saccades made before instructional cue processing) than controls. Control participants exhibited lower microsaccade rates during the fixation epoch preceding correct anti- vs. prosaccade initiation, but this task-related modulation was absent in both patient groups. Regarding emotion processing, the ADHD group performed worse than controls on trials with neutral faces, while the BD group performed worse than controls on trials with faces of all valence. These findings suggest that response inhibition, mediated by the fronto-striatal circuitry, is a central deficit in both ADHD and BD. This deficit is exacerbated in BD during emotion processing, presumably mediated by dysregulated limbic circuitry involving the anterior cingulate and orbitofrontal cortex. Better understanding of the interplay of these brain circuits will help identify behavioral markers in these two disorders.