Rejection sensitivity has been found to predict the course of unipolar depression as well as key outcomes, but has not yet been considered within bipolar disorder. The present study investigated the effects of rejection sensitivity on outcome in bipolar disorder. Fifty-three participants diagnosed with bipolar I disorder in remission using the Structured Clinical Interview for DSM-IV were compared to 44 controls with no history of mood disorder. A subset of 38 bipolar participants completed follow-up interviews using standard symptom severity measures at 6 months. People with bipolar I disorder reported higher rejection sensitivity scores than did controls. Within the bipolar sample, rejection sensitivity at baseline predicted increases in depression, but not mania, over the following 6 months; heightened rejection sensitivity was also correlated with poorer quality of life, social support, and psychological well-being. Findings highlight the importance of interpersonal-cognitive factors for treating depression and improving outcome within bipolar I disorder.