This article presents a case study of a 31-year-old woman with a dual diagnosis of Borderline Personality Disorder (BPD) and Eating Disorder Not Otherwise Specified (EDNOS). Paula received a 12-month Dialectical Behavior Therapy (DBT) outpatient treatment. DBT is considered a transdiagnostic treatment approach to address emotion dysregulation, which shifts the therapy focus traditionally placed only on behavioral change towards including also validation and acceptance and dialectical strategies. DBT addresses eating symptomatology as a dysfunctional form of emotional regulation and has shown promising results regarding its efficacy for the treatment of BPD and EDNOS comorbidity. Given the growing evidence, a standard DBT treatment plan was developed for this case. Specifically, pre-treatment and phase 1 of the DBT program are described. During pre-treatment and phase 1, individual therapy aims to improve and maintain client’s motivation to change and engage in treatment, as well as to establish and prioritize treatment goals. As for group therapy, the main goal of the skills training in DBT is to enhance individual’s capability by increasing skillful behavior (mindfulness, emotion regulation, distress tolerance and interpersonal effectiveness skills). Paula received 24 weekly skills training sessions over a year. The results after a 12-month standard DBT treatment showed that Paula no longer met criteria for BPD, she had a significant decrease in difficulties in emotional regulation and impulsiveness and in EDNOS symptomatology. This case study may enhance learning about how to apply a transdiagnostic treatment to address BPD and EDNOS together in clinical practice.