Emotion dysregulation is a core feature of bipolar disorder (BD) that persists into periods of remission. Neuroimaging studies show aberrant neural responses during emotion regulation (ER) in patients with BD relative to healthy controls, but behavioural evidence for ER deficits is sparse and conflicting. This study aimed to explore ER in BD using a novel, personally relevant experimental paradigm. Twenty patients with BD and 20 patients with unipolar disorder (UD), in full or partial remission, and 20 healthy controls were given a novel computerised test. Participants were instructed to react naturally or dampen their emotional response to positive and negative social scenarios and associated self-beliefs. They were also given an established experimental task for comparison, involving reappraisal of negative affective picture stimuli, as well as a questionnaire of habitual ER strategies. BD patients showed reduced ability to down-regulate emotional responses in negative, but not positive, social scenarios relative to healthy controls and UD patients. In contrast, there were no between-group differences in the established ER task or in self-reported habitual reappraisal strategies. Findings highlight the novel social scenario paradigm as a sensitive test for detection of ER difficulties in BD.