Psychological treatments for young people with sub-threshold or full-syndrome borderline personality disorder (BPD) are found to be effective. However, little is known about the age at which adolescents benefit from early intervention. This study investigated whether age affects the effectiveness of early intervention for BPD.

N = 626 participants (M age = 15 years, 82.7% female) were consecutively recruited from a specialized outpatient service for early intervention in BPD in adolescents aged 12- to 17-years old. DSM-IV BPD criteria were assessed at baseline, one-year (n = 339) and two-year (n = 279) follow-up.

Older adolescents presented with more BPD criteria (χ2 (1) = 58.23, p < 0.001) and showed a steeper decline of BPD criteria over the 2-year follow-up period compared with younger adolescents (χ2 (2) = 13.53, p = 0.001). In an attempt to disentangle effects of early intervention from the natural course of BPD, a parametrized regression model was used. An exponential decrease (b = 0.10, p < 0.001) in BPD criteria was found when starting therapy over the 2-year follow-up. This deviation from the natural course was impacted by age at therapy commencement (b = 0.06, p < 0.001), although significant across all ages: older adolescents showed a clear decrease in BPD criteria, and young adolescents a smaller decrease.

Early intervention appears effective across adolescence, but manifests differently: preventing the normative increase of BPD pathology expected in younger adolescents, and significantly decreasing BPD pathology in older adolescents. The question as to whether developmentally adapted therapeutic interventions could lead to an even increased benefit for younger adolescents, should be explored in future studies.

Nonsuicidal self-injury (NSSI) is prevalent in adolescent clinical samples. There is evidence that NSSI can be treated effectively but data on individual treatment outcomes is limited. The goal of this study was to examine response, remission, exacerbation, and relapse rates over one and two years, respectively, among a clinical sample of adolescents with NSSI. Furthermore, we aimed to identify clinically relevant predictors of NSSI trajectories.

The sample consists of n = 203 adolescents (12–17 y., 94% female) from a specialized outpatient clinic for risk-taking and self-harming behavior with NSSI on at least five days in the six months before first assessment. Assessments were completed at baseline and one (FU1) and two (FU2) years later using structured clinical interviews and self-report questionnaires.

At FU1, 75% reported a reduction in NSSI frequency by at least 50% (treatment response); among those, one third (25% of the entire sample) achieved a remission (0 NSSI); an exacerbation (⩾50% more NSSI) was observed in 11% of patients. Of those in remission, 41% relapsed one year later. Predictors of non-response or non-remission were inpatient treatment and depressive symptoms. Adolescents with lower NSSI frequency at baseline had a higher risk of exacerbation. Due to limited sample size at FU2 no prediction model for relapse was established.

While most adolescents presenting with NSSI achieved significant improvement, more attention should be paid to the rather low rates of full remission. Prediction and early detection of individuals who deteriorate during or relapse after treatment is critical.