This study sought to extend extant research on the association between borderline personality (BP) pathology and at-risk parenting by examining the dynamic nature of parenting in response to infant distress in mothers with and without clinically relevant levels of BP pathology. Findings revealed that mothers with clinically relevant levels of BP pathology were less likely than those without BP pathology to display positive affect in response to infant distress. There were no differences in the overall likelihood of insensitive parenting behaviors as a function of BP pathology, either in general or in response to infant distress. However, consistent with literature emphasizing the transactional nature of parent–child relationships, findings revealed that the likelihood of insensitive parenting behaviors among mothers with clinically relevant levels of BP pathology changed over time, increasing significantly as infant distress persisted for longer durations (a pattern not present for mothers without BP pathology). Moreover, maternal responses to infant distress were found to influence infant distress, with the likelihood of infant distress decreasing after maternal positive affect and increasing after maternal insensitive behaviors. The implications of findings for understanding the mechanisms of risk for children of mothers with BP pathology, as well as the transactional nature of mother-infant relationships in general, are discussed.