Abstract: Among those with borderline personality disorder (BPD), dialectical behavior therapy (DBT) is considered a frontline treatment for reducing impulsivity and suicidality and improving emotion regulation. DBT has been proven effective when delivered within Veterans Health Administration. Much of the research supporting the use of DBT was conducted on patients with relatively clean diagnostic profiles (e.g. excluding bipolar disorder). However, Veterans are diagnostically complex and are especially likely to have comorbid posttraumatic stress disorder (PTSD). We sought to understand how a PTSD diagnosis affected treatment outcomes among Veterans who presented for full-model DBT treatment. In a sample of 62 Veterans, half of whom had probable (N=24) or confirmed (N=7) PTSD, we tested whether comorbid PTSD and BPD affected baseline severity, treatment engagement, or treatment outcomes. Compared to those without PTSD, BPD-PTSD did not hamper treatment engagement and was unrelated to BPD symptom severity at baseline. BPD-PTSD was associated with noninferior and indeed sharper reductions in BPD symptoms throughout treatment. That is, relative to Veterans without PTSD, Veterans with co-occurring PTSD and BPD symptoms reported steeper symptom reductions. Altogether, our findings support the use of DBT in Veterans who present with both BPD symptoms and PTSD.