Existing literature on the effects of borderline personality disorder (BPD) and eating disorder (ED) comorbidity in terms of clinical presentation and treatment outcome has been limited and inconclusive. The present study examined whether clients with EDs and varying levels of BPD symptoms presented with more severe ED symptoms at admission, and whether they responded to dialectical behavior therapy (DBT)-based treatment. Participants (N = 176) were adults in a DBT-based partial hospitalization program for EDs at an academic medical center. Participants completed self-report measures at admission, 1-month postadmission, discharge, and 6-month follow-up. Results suggested that patients with elevated BPD symptoms at admission had greater ED symptoms during treatment, evidenced by small to moderate effect sizes. However, patients with high BPD symptoms demonstrated steeper declines in binge eating, fasting, and parasuicidal behavior early during treatment compared to patients with low BPD symptoms. Individuals with high BPD symptoms at admission (i.e., probable BPD diagnosis) were as likely to meet remission criteria and relapse as individuals with low BPD symptoms, though this null finding may be influenced by small cell sizes. Our findings also suggest that DBT skills use does not predict changes in symptoms. In sum, our findings suggest that while clients with higher BPD symptoms may improve during DBT-based partial hospitalization, their ED symptoms may remain more severe. Future studies are needed to determine whether adjunctive treatments improve outcomes for clients with EDs and comorbid BPD symptoms in DBT programs and whether skills use quality is a better predictor of ED symptom changes. (PsycInfo Database Record (c) 2024 APA, all rights reserved).