BackgroundState and trait dissociation are associated with borderline personality disorder (BPD) severity and severity of commonly co-occurring mental health symptoms. Although these distinct constructs do not consistently co-occur in experimental settings, they are frequently reported as the same construct, namely dissociation. This study aimed to investigate the co-occurrence of state and trait dissociation among young people with BPD and to examine whether state or trait dissociation were associated with symptom severity in this population.MethodsState dissociation was induced using a stressful behavioural task in a clinical sample of 51 young people (aged 15–25 years) with three or more BPD features. Diagnoses, state and trait dissociation, BPD severity and severity of posttraumatic stress disorder (PTSD), depressive, and stress symptoms were assessed by self-report or research interview.ResultsA chi-square test of independence showed a strong association between state and trait dissociation. Bonferroni correctedt-tests showed that state dissociation was significantly associated with PTSD symptom severity and likely associated with BPD severity and severity of depressive and stress symptoms. Trait dissociation was not associated with symptom severity or severity of BPD features.ConclusionsThese findings highlight the need to distinguish between state and trait dissociation in personality disorder research. They suggest that state dissociation might be an indicator of higher severity of psychopathology in young people with BPD.