We examined event-contingent recording of daily interpersonal interactions in a diagnostically diverse sample of 101 psychiatric outpatients who were involved in a romantic relationship. We tested whether the unique effect of borderline personality disorder (BPD) symptoms on affective responses (i.e., hostility, sadness, guilt, fear, and positive affect) to perceptions of rejection or acceptance differed with one's romantic partner compared with nonromantic partners. BPD symptoms were associated with more frequent perceptions of rejection and less frequent perceptions of acceptance across the study. For all participants, perceptions of rejecting behavior were associated with higher within-person negative affect and lower within-person positive affect. As predicted, in interactions with romantic partners only, those with high BPD symptoms reported heightened hostility and, to a lesser extent, attenuated sadness in response to perceptions of rejection. BPD symptoms did not moderate associations between perceptions of rejection and guilt, fear, or positive affect across romantic and nonromantic partners. For all participants, perceived acceptance was associated with lower within-person negative affect and higher within-person positive affect. However, BPD symptoms were associated with attenuated positive affect in response to perceptions of accepting behavior in interactions with romantic partners only. BPD symptoms did not moderate associations between perceptions of acceptance and any of the negative affects across romantic and nonromantic partners. This study highlights the specificity of affective responses characteristic of BPD when comparisons are made with patients with other personality and psychiatric disorders. Implications for romantic relationship dysfunction are discussed. (PsycINFO Database Record