This study sought to build upon existing research on interpersonal sensitivity in borderline personality disorder (BPD) by examining whether emotion dysregulation mediates the relationship between BPD and cognitive and emotional responses to social rejection. Participants with (n = 53) and without (n = 34) BPD reported on levels of negative affect and threat to four social needs (perceived control, belonging, selfesteem, and meaningful existence) in response to a laboratory-based social ostracism task (Cyberball). Results revealed heightened interpersonal (rejection) sensitivity among BPD (vs. non-BPD) participants, as evidenced by heightened threat to all social needs and nonspecific distress (although not overall negative affect) in response to the task. Furthermore, both overall emotion dysregulation and the specific dimensions involving emotion modulation strategies, emotional clarity, and the control of behaviors when distressed mediated the relationship between BPD status and several cognitive (threats to meaningful existence, belonging, and self-esteem) and emotional (nonspecific distress) responses to the task.