Complex posttraumatic stress disorder (CPTSD) has been included as a diagnostic category in the International Classification of Diseases, 11th Edition, consisting of six symptom clusters: the three PTSD criteria of reexperiencing, avoidance, and hypervigilance, in addition to three disturbances of self-organization (DSO) symptoms defined as emotional dysregulation, interpersonal difficulties, and negative self-concept. As borderline personality disorder (BPD) shares similar features to DSO presentations and is commonly associated with PTSD, there is debate as to whether and how CPTSD is distinct from PTSD comorbid with BPD. This article aimed to identify groups with distinct profiles of self-reported CPTSD and BPD symptoms and associated trauma history characteristics. A latent class analysis (LCA) using CPTSD and BPD symptom variables was conducted on a sample of 195 treatment-seeking adults at a specialist trauma service. The classes were then compared on demographic and clinical characteristics using a series of analysis of variance and χ2 tests. The latent class analysis determined three distinct classes: a CPTSD/High BPD class characterized by high symptom endorsement across both conditions, a CPTSD/Moderate BPD class characterized by high PTSD and DSO symptom endorsement and moderate BPD, and a PTSD/Low BPD class characterized by PTSD symptoms and low DSO and BPD symptom endorsement. The two CPTSD classes were associated with greater exposure to multiple, interpersonal traumas earlier in life and exhibited higher functional impairment. Findings support the construct of a CPTSD diagnosis as a separate entity although BPD features seem to overlap greatly with CPTSD symptoms in this highly traumatized clinical sample. (PsycINFO Database Record (c) 2019 APA, all rights reserved).