Borderline personality disorder (BPD) manifests in adolescents, serving as a forerunner for later dysfunctionality and life constraints. BPD is characterized by multiple difficulties in understanding the self and others, and it has been implied that intrapsychic processes of reasoning might be the primary driver of these disturbances. In this study, we examined the role of narrative identity, the dynamic and evolving story people construct about their personal pasts, presents, and futures, as a potentially important but largely overlooked aspect of temporal reasoning within the intrapsychic system of adolescents with BPD features. A total of 174 American inpatient adolescents (Mage = 15.12 years, SD = 1.52) completed self-report measures of BPD upon hospital admission. Adolescents' narrative identity (i.e., themes/future wishes of agency and communion), mentalizing, and emotion dysregulation were assessed. Results showed that narrative identity (i.e., thwarted themes of agency and communion) was associated with lower mentalizing and higher emotional dysregulation capacities, supporting narrative identity's relation to other relevant aspects of intrapsychic processes of reasoning in BPD. Regression analyses showed that both higher levels of emotion dysregulation and more thwarted narrative themes of agency (but not mentalizing) were significantly associated with BPD features. Intriguingly, narrative identity (i.e., thwarted themes of agency) showed incremental validity in accounting for features of BPD, over and above emotion dysregulation. It is concluded that disturbances related to narrative identity might be a prominent component of the intrapsychic reasoning system in BPD and should be included in future work on the topic. (PsycInfo Database Record (c) 2022 APA, all rights reserved).