OBJECTIVEAbout half of individuals seeking treatment for borderline personality disorder (BPD) present with co-occurring posttraumatic stress disorder (PTSD). However, therapies that have been proven efficacious for simultaneously treating the full spectrum of core symptoms in patients with a dual diagnosis of BPD + PTSD are lacking.METHODThis is a subgroup analysis from a randomized controlled trial (registration number DRKS00005578) which compared the efficacy of two treatment programs, dialectical behavior therapy for PTSD (DBT-PTSD) versus cognitive processing therapy (CPT). Specifically, the present analysis was carried out in 93 women with a dual diagnosis of BPD + PTSD (Diagnostic and Statistical Manual for Mental Disorders; DSM-5). Outcome evaluations included the Clinician-Administered PTSD Scale, the Borderline Symptom List, and validated scales assessing dissociation, depression, and global functioning. The primary analysis was based on the intent-to-treat population, using mixed models.RESULTSBoth PTSD and BPD symptoms significantly decreased in both treatment groups. For PTSD symptoms, pre-post effect sizes were d = 1.20, 95% confidence interval (CI): [0.80-1.58] in the DBT-PTSD group and d = 0.90, 95% CI: [0.57-1.22] in the CPT group; for BPD symptoms, they were d = 1.17, 95% CI: [0.77-1.55], and d = 0.50, 95% CI: [0.20-0.79], respectively. Between-group comparisons significantly favored DBT-PTSD for improvement in symptoms of PTSD, BPD, and dissociation. Between-group differences regarding depression and global functioning were not significant.CONCLUSIONBoth DBT-PTSD and CPT emerged as promising treatment options for simultaneously addressing the full spectrum of core symptoms in patients diagnosed with BPD + PTSD. Differential efficacy was in favor of DBT-PTSD as participants randomized to the DBT-PTSD arm improved more with respect to both their BPD and PTSD symptoms. (PsycInfo Database Record (c) 2021 APA, all rights reserved).