Background: This study aimed to identify personality features characterizing adolescent girls and boys with borderline personality disorder (BPD) and to see whether meaningful patterns of heterogeneity exist among adolescents diagnosed with the disorder. Methods: Two hundred and ninety-four randomly selected doctoral-level clinicians described adolescent patients using Axis II rating scales and the Shedler-Westen Assessment Procedure-200 for Adolescents (SWAP-200-A). We used the SWAP-200-A to provide empirically derived descriptions of female and male adolescents meeting DSM-IV criteria for BPD (who differed substantially in their profiles), and used Q-factor analysis to identify naturally occurring groupings of female patients based on shared personality features. Results: The symptoms and phenomenology of adolescent girls with BPD are similar to those of adults. Adolescent boys meeting BPD criteria have a more aggressive, disruptive, antisocial presentation. Although "N"s did not permit further analysis of the data on adolescent boys, Q-analysis isolated four clinically coherent subgroups of girls with BPD: high-functioning internalizing, histrionic, depressive internalizing, and angry externalizing. Conclusions: BPD in female adolescents resembles DSM-IV BPD as defined for adults. The operating characteristics of the DSM-IV criteria for adolescent boys require further investigation. Empirically derived subgroups are similar to those identified in recent research with adult females. Differences across subgroups on internalizing and externalizing Child Behavior Checklist (CBCL) scales provide preliminary data on the validity of subgroups and raise questions about the place of BPD among internalizing and externalizing spectrum disorders.