Objective: Interpersonal dysfunction is a hallmark feature of borderline personality disorder (BPD). Representing lifelong relational patterns based in internal representations, quality of object relations (QOR) has been theorized as a core aspect of borderline personality pathology; yet empirical inquiry of this relationship has been limited. The present study investigated the association between QOR and BPD in the context of other salient correlates of BPD. Method: Participants were 137 outpatients obtaining care at an intensive treatment program for patients with personality dysfunction. BPD was assessed using two interview-based instruments. A separate interviewer-rated assessment of quality of object relations was administered by a different set of assessors. Participants also completed self-report measures of symptom distress, five-factor personality, and dysphoric affects. Results: Regarding BPD severity, QOR emerged as the only significant predictor with all variables in the model. Similarly, logistic regression found that QOR was associated with a significantly greater likelihood of having a diagnosis of BPD, after accounting for the effects of the other variables in the model. Conclusion: QOR is significantly and uniquely associated with BPD, suggesting that internalized representations of self and others play an important role underlying BPD pathology.