Background
Studies of the medium- to long-term clinical and functional course for treatment-seeking adolescents with borderline personality disorder (BPD) are lacking. This study aims to outline the psychopathological and functional status of participants, five years after being diagnosed with BPD during adolescence.

Methods
Participants were originally enrolled in a randomized clinical trial that compared mentalization-based group treatment with treatment as usual for adolescents with BPD. Semi-structured interview assessments at five-year follow-up included the Schedules for Clinical Assessment in Neuropsychiatry and the Structured Clinical Interview for DSM-5 Personality Disorders. Attention deficit hyperactivity disorder (ADHD), alcohol, substance and tobacco use, posttraumatic stress disorder (PTSD), complex PTSD, and general functioning were assessed using self-report instruments.

Results
97 of the original sample of 111 participants (87%) participated. They were aged 19–23 years. The most prevalent disorders were ADHD (59%), any personality disorder (47%) of which half continued to meet criteria for BPD (24%), anxiety disorders (37%), depressive disorders (32%), PTSD or complex PTSD (20%), schizophrenia (16%), and eating disorders (13%). Only 16% did not meet criteria for any mental disorder. Approximately half of the sample were in psychological and/or psychopharmacological treatment at the time of follow-up. Their general functioning remained impaired, with 36% not engaged in education, employment or training (NEET), which is nearly four times the rate of NEET in the same age group in the general population.

Conclusions
Although stability of the categorical BPD diagnosis is modest, adolescents meeting diagnostic criteria for BPD show a broad range of poor outcomes at five-year follow-up. BPD appears to be a marker of general maladjustment during adolescence and a harbinger of severe problems during the transition to young adulthood. Early intervention programs for adolescents diagnosed with BPD should focus upon a broad range of functional and psychopathological outcomes, especially social and vocational support, rather than the narrow BPD diagnosis.