Poor relationship quality common among individuals with borderline personality disorder (BPD) may result, in part, from biased interpersonal decision-making. We examined memory biases for hypothetical interpersonal partner choices varying in the degree of familiarity. In Part 1 of our study, participants (n = 192) were asked to choose between novel or familiar partners based on lists of traits across six vignettes, and in Part 2, they completed a trait recognition task 36-60 hours later. Lower perceived social support was associated with a memory bias toward novel (over familiar) partners. BPD features were negatively related to an overall interpersonal memory bias (i.e., remembering both partners more negatively). However, when accounting for idiographic valence ratings, BPD features were positively related to this bias among those also low in social support. Memory biases may be related to partner choices associated with BPD features; however, it is critical to assess the role of perceived social support.