This study investigated whether deficits in mindfulness (attention, awareness, and acceptance of the present moment) underlie variability in borderline personality disorder (BPD) features and related impairments in interpersonal functioning, impulsivity, and emotion regulation. A path analytic approach was used to examine the relationships of trait mindfulness with BPD features, interpersonal effectiveness, impulsive and passive emotion-regulation, and neuroticism in a psychiatric sample of adults (N = 70). As hypothesized, mindfulness was associated inversely with BPD features and core areas of dysfunction, and these associations continued when controlling for neuroticism. Furthermore, mindfulness deficits continued to predict BPD features even when interpersonal effectiveness, passive and impulsive emotion-regulation, and neuroticism were controlled. These findings suggest that mindfulness may be a unique predictor for the expression of BPD pathology. An emphasis on mindfulness may thus be crucial in enhancing the formulation and treatment of BPD.