Although research on the temperamental vulnerabilities associated with borderline personality disorder (BPD) has focused primarily on the role of impulsive-aggression, affective instability, and emotional vulnerability, growing evidence suggests that anxiety sensitivity (AS) also may increase vulnerability for BPD. This study provides preliminary data on the relationship between AS and BPD, examining whether AS distinguishes outpatients with BPD from outpatients without a personality disorder (non-PD), and whether the relationship between AS and BPD is mediated by experiential avoidance (i.e., attempts to avoid unwanted internal experiences, such as anxiety). Findings indicate that BPD outpatients reported higher levels of AS than non-PD outpatients and AS reliably distinguished between these two groups. Furthermore, the relationship between AS and BPD was mediated by experiential avoidance. Finally, results indicate that AS (and experiential avoidance as a mediator) accounted for a significant amount of additional variance in BPD status above and beyond both negative affect and two well-established temperamental vulnerabilities for BPD (affect intensity/reactivity and impulsivity). Findings suggest the need to further explore the role of AS in the pathogenesis of BPD.