BackgroundExecutive functions (EF) consolidate during adolescence and are impaired in various emerging psychiatric disorders, such as pediatric Major Depressive Disorder (pMDD) and Borderline Personality Disorder. Previous studies point to a marked heterogeneity of deficits in EF in pMDD. We examined the hypothesis that deficits in EF in adolescents with pMDD might be related to comorbid Borderline Personality features (BPF).MethodsWe examined a sample of 144 adolescents (15.86 ± 1.32) diagnosed with pMDD. Parents rated their child’s EF in everyday life with the Behavior Rating Inventory of Executive Function (BRIEF) and BPF with the Impulsivity and Emotion Dysregulation Scale (IED-27). The adolescents completed equivalent self-rating measures. Self- and parent-ratings of the BRIEF scores were compared with paired t-Tests. Correlation and parallel mediation analyses, ICC, and multiple regression analyses were used to assess symptom overlap, parent-child agreement, and the influence of depression severity.ResultsOver the whole sample, none of the self- or parent-rated BRIEF scales reached a mean score above T > 65, which would indicate clinically impaired functioning. Adolescents tended to report higher impairment in EF than their parents. Depression severity was the strongest predictor for BPF scores, withEmotional Controlpredicting parent-rated BPF andInhibitpredicting self-rated BPF. Furthermore, the Behavioral Regulation Index, which includes EF closely related to behavioral control, significantly mediated the relationship between depression severity and IED-27 factorsemotional dysregulationandrelationship difficultiesbut notnon-suicidal self-injuries.ConclusionOn average, adolescents with depression show only subtle deficits in executive functioning. However, increased EF deficits are associated with the occurrence of comorbid borderline personality features, contributing to a more severe overall psychopathology. Therefore, training of executive functioning might have a positive effect on psychosocial functioning in severely depressed adolescents, as it might also improve comorbid BPF.Clinical trial registrationwww.ClinicalTrials.gov, identifier NCT03167307.