Journal of Personality Disorders, 32, 1-11, 2018 © 2018 The Guilford Press 1 From Orygen, The National Centre of Excellence in Youth Mental Health, Parkville, Australia (K. N. T., M. C., J. B., M. J., A. M. C.); Centre for Youth Mental Health, The University of Melbourne, Melbourne, Australia (K. N. T., M. C., J. B., M. J., A. M. C.); School of Psychological Sciences, The University of Melbourne (H. J.); and Orygen Youth Health, Melbourne, Australia (L. M., M. J., A. M. C.) Address correspondence to Professor Andrew Chanen, Orygen, the National Centre of Excellence in Youth Mental Health, Locked Bag 10, Parkville VIC 3052, Australia. E-mail: andrew.chanen@orygen. org.au CLINICAL SIGNIFICANCE OF SUBTHRESHOLD BPD FEATURES THOMPSON ET AL. THE CLINICAL SIGNIFICANCE OF SUBTHRESHOLD BORDERLINE PERSONALITY DISORDER FEATURES IN OUTPATIENT YOUTH Katherine N. Thompson, PhD, Henry Jackson, PhD, Marialuisa Cavelti, PhD, Jennifer Betts, DPsych, Louise McCutcheon, DPsych, Martina Jovev, PhD, and Andrew M. Chanen, MBBS, PhD, FRANZCP Studies among adult patients have found that subthreshold borderline personality disorder (BPD) features are associated with elevated psycho- social morbidity compared with patients with no BPD features. However, the clinical significance of subthreshold features of BPD has not been investigated among real-world patients during the clinical emergence of the disorder, which is usually between puberty and emerging adulthood. This study aimed to replicate and extend previous research by comparing outpa- tient youth aged 15–25 years with subthreshold BPD features with youth with no BPD features. The sample included 499 potential participants, of whom 111 had no DSM-IV BPD features at all, and 155 had between one and four features. Results indicated that the group with subthreshold BPD features had more severe mental illness and poorer social and occupational functioning. These findings suggest that subthreshold BPD features are clinically important and should be a focus of clinical intervention to reduce continuing disability and improve outcome. Keywords: borderline personality disorder, subthreshold, social occupational functioning, youth, adolescence, psychiatry Although the fifth edition of the Diagnostic and Statistical Manual of Men- tal Disorders (DSM-5; American Psychiatric Association [APA], 2013) has continued the tradition of syndrome-based categorical diagnosis of person- ality disorder, it is widely acknowledged (including in the alternative model in section III of the DSM-5) that the threshold for distinguishing patients with and without a personality disorder is arbitrary and that there is no