Many studies have determined that the traits of emotional dysregulation, negative affect, and impulsivity are the strongest predictors of borderline personality disorder (BPD). Although psychodynamic, empirically supported BPD treatments (i.e., transference-focused, mentalization based) focus upon changing the internal representations of self and other, no studies have simultaneously evaluated the contribution of object relations in relation to these traits in predicting BPD symptoms. This study sought to determine the combined effects of emotional dysregulation, negative affect, impulsivity, and object relations in the prediction of BPD through the use of mediation modeling in 4 a priori hypothesized relationships among these variables. One hundred sixty-nine psychiatric outpatients and 171 undergraduate students were evaluated with self-reported trait and object relations measures and were administered 2 semistructured diagnostic interviews for BPD. Although all trait and object relations measures were correlated with BPD symptoms, the best fitting model was one in which object relations partially mediated the relationship of negative affect and impulsivity with BPD symptoms. Direct effects of the traits were also observed in mediation. Self-reported object relational quality had more of an effect on the prediction of BPD than previously recognized within a trait-framework, thus further supporting the model explicated in psychodynamic and relationally based treatments for BPD.