Prevalence data on self-mutilation and suicide attempts for adolescent borderline personality disorder (BPD) are currently not available. The purpose of this paper was to determine the frequency and methods of two forms of physically self-destructive acts (i.e. self-mutilation and suicide attempts) reported by adolescent borderline inpatients in one of the largest samples to date and to compare these results with a similarly diagnosed and assessed group of adult borderline inpatients. A total of 104 adolescent inpatients with BPD and 290 adult inpatients with BPD were interviewed about their lifetime history of physically self-destructive acts. The overall rates of self-mutilation (about 90%) and suicide attempts (about 75%) were similar during index admission for both adolescent and adult borderline patients. However, adolescents reported significantly higher rates of extreme levels of lifetime self-mutilation (e.g. >25 and >50 episodes) and cutting in particular, as compared with adult BPD. In contrast, borderline adults were significantly more likely to report a history of numerous (five or more) suicide attempts than adolescents with BPD. Self-mutilation and suicide attempts among adolescent borderline patients are prevalent and serious. Taken together, these results suggest that extreme levels of self-mutilation distinguish adolescent BPD from adults with BPD. Copyright © 2017 John Wiley & Sons, Ltd.