The newly added diagnosis complex posttraumatic stress disorder (CPTSD) in the 11th edition of the International Classification of Diseases (ICD-11) includes a domain of disturbances in self-organization (DSO), in addition to PTSD. The DSO construct appears to have definitional overlap with the dimensional personality pathology severity measure, personality functioning. This study investigated the association between personality functioning and ICD-11 CPTSD, and the associations between DSO clusters and personality functioning domains. The sample comprised 83 outpatients with ICD-11 PTSD or CPTSD. Personality functioning was operationalized with the Level of Personality Functioning Scale (LPFS) and assessed with the Structured Clinical Interview for the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Alternative Model for Personality Disorders, Module I. Results showed an average level of moderate impairment in personality functioning (i.e., Identity, Self-Direction, Empathy, and Intimacy) for the whole sample. However, the levels of impairment in personality functioning were significantly more severe in patients with ICD-11 CPTSD, compared with patients with PTSD. Furthermore, the results revealed strong significant positive associations between the personality functioning domains and the DSO symptom clusters, except for the LPFS Identity domain and the DSO Affective Dysregulation cluster. Contrary to expectations, we found a significant positive association between the PTSD symptom cluster Avoidance and the LPFS domains Identity, Self-Direction, and Intimacy. Furthermore, higher levels of impairment in the Identity and Intimacy domain were associated with an increase in DSO symptom severity. New development in assessment of personality functioning may assist clinicians in differential diagnosis of PTSD and CPTSD.