BackgroundComplex Post-Traumatic Stress Disorder (CPTSD) and Emotionally Unstable Personality Disorder (EUPD) have shared aetiology and symptomatology, and are associated with multiple comorbidities and poor clinical outcomes. Evidence from studies with clinical populations indicates high levels of morbidity between the two diagnoses. Yet, the cumulative impact of coexisting CPTSD and EUPD diagnoses on levels of general distress, risk, quality of life and resulting treatment needs have not been explored. Accordingly, our understanding of the impact of experiencing both disorders and the relationship between coexisting trauma responses, and associated treatment needs remains limited. MethodologyUsing a convenience sample of 47 women admitted to a specialised DBT inpatient service, associations between general distress, risk, quality of life and diagnostic status were explored. ResultsWomen with comorbid EUPD and CPTSD reported significantly higher levels of general distress and risk to self, and significantly lower quality of life compared to women with EUPD alone. Hierarchical regression analyses revealed that, when exploring the isolated effect of each symptom cluster, only affective dysregulation remained a significant predictor of distress, risk to self, and quality of life (all p < .05). ConclusionsAlthough our results require further replication, the current study indicates that the experience of comorbid EUPD and CPTSD is impactful. Affect regulation may play a critical role in explaining comorbidity between EUPD and CPTSD. Accordingly, the current findings offer novel insights into the relationship between the two diagnoses, with clinical and theoretical consequences explored.