Background: The formulations of post-traumatic stress disorder (PTSD) and the newly included disorder complex PTSD (CPTSD) in the 11th edition of the International Classification of Diseases (ICD-11) have not been evaluated on a broad range of maladaptive personality traits. Objective: The aim of this study was to evaluate ICD-11 PTSD and CPTSD on maladaptive personality traits. Method: In a cross-sectional study of 106 Danish outpatients with ICD-10 PTSD, we used the International Trauma Questionnaire (ITQ) to identify patients with either ICD-11 PTSD or CPTSD (N = 84). We utilized the Personality Inventory for DSM-5 (PID-5) from the alternative model of personality disorders in DSM-5, section III, to evaluate personality trait differences between ICD-11 PTSD and CPTSD. Furthermore, PID-5 was also used to investigate relationships between personality traits and ICD-11 PTSD/CPTSD symptom clusters. The Life Event Checklist was used to assess traumatic experiences, and the MINI International Neuropsychiatric Interview was applied to assess comorbidity. Results: Patients with ICD-11 PTSD or CPTSD had elevated scores on personality traits indicative of internalizing psychopathology. However, higher impairment levels of the trait domains Negative Affectivity (d= 0.75) and Psychoticism (d = 0.80) discriminated patients with ICD-11 CPTSD from patients with PTSD. The PID-5 trait domain Detachment was moderately positively correlated to most of the ITQ symptom clusters and, the ITQ Negative Self-concept symptom cluster showed a relatively high number of significant correlations across all the PID-5 trait domains and facets. The PID-5 domain Negative Affectivity and almost all the encompassing facets were significantly correlated with DSO symptom clusters. Conclusions: The findings demonstrate the relevance of applying dimensional assessment of personality features to study the psychopathology of ICD-11 PTSD and CPTSD and potential differences. The results suggest that CPTSD is a more debilitating disorder than PTSD considering the severity of the personality features.