Background The diagnosis of complex posttraumatic stress disorder (CPTSD) was included in the 11th revised edition of the International Classification of Diseases (ICD-11). CPTSD shares trauma-specific symptoms with its sibling disorder PTSD but is additionally characterized by disturbances of the individual’s self-organization (DSO). The clinical utility of the CPTSD diagnosis has yet to be thoroughly investigated. Objective The current study aimed to examine the clinical utility of the CPTSD diagnosis, considering the upcoming implementation of ICD-11 in clinical practice. Method International field studies, construct- and validity analyses leading up to the inclusion in ICD-11 are reviewed, and the diagnostic measures; International Trauma Questionnaire (ITQ) and International Trauma Interview (ITI) are presented. Also, the relationship between CPTSD and borderline personality disorder (BPD) is elaborated in an independent analysis, to clarify their differences in clinical relevance to treatment. Treatment implications for CPTSD are discussed with reference to existing guidelines and clinical needs. Results The validation of ITQ and ITI contributes to the cementation of CPTSD in further clinical practice, providing qualified assessment of the construct, with intended informative value for both clinical communication and facilitation of treatment. CPTSD is found distinguishable from both PTSD and BPD in empirical studies, while the possibility of comorbid BPD/PTSD cases being better described as CPTSD is acknowledged. Practitioners need to employ well-established methods developed for PTSD, while considering additional DSO-symptoms in treatment of CPTSD. Conclusions The inclusion of CPTSD in ICD-11 may potentially facilitate access to more tailored treatment interventions, as well as contribute to increased research focus on disorders specifically associated with stress. The clinical utility value of this additional diagnosis is expected to reveal itself further after ICD-11 is implemented in clinical practice in 2022 and onwards. Yet, CPTSD’s diagnostic inclusion gives future optimism to assessing and treating complex posttraumatic stress symptoms.