The complexity of posttraumatic stress disorder (PTSD) symptoms related to childhood abuse (CA) present challenges for effective psychotherapeutic treatment. Consequently, there is great interest in the long-term effectiveness of psychological treatments for this population. This study aims to investigate the long-term outcomes of Dialectical Behaviour Therapy for PTSD (DBT-PTSD) and Cognitive Processing Therapy (CPT) 9 months after treatment termination. This is a long-term analysis from a randomised-controlled trial of DBT-PTSD versus CPT (registration number DRKS00005578). Initially, 193 individuals with CA-related PTSD were randomly allocated to receive either DBT-PTSD ( = 98) or CPT ( = 95). The primary outcome the Clinician-administered PTSD-Scale for DSM-5 (CAPS-5) was administred at baseline, treatment completion (15 months post-randomization) and at the 9-month follow-up. Secondary outcomes included self-reported PTSD severity (PCL-5), dissociation (DSS), severity of borderline symptoms (BSL-23), and psychosocial functioning (GAF). No significant changes were observed in the primary (CAPS) and all other outcomes from post-intervention to 9-months follow-up in both the DBT-PTSD (CAPS:  = 15.60, = 14.93) and CPT group (CAPS:  = 18.80,  = 17.41). Between-group analyses at 9-months follow-up were significantly in favour of DBT-PTSD compared to CPT with small to medium effect sizes on all outcomes ranging from = 0.35 on the CAPS to = 0.57 on the BSL-23 and GAF. Our results indicate that treatment effects of psychotherapy addressing complex presentations of PTSD persist 9 months after treatment termination. In addition, the superiority of DBT-PTSD as compared to CPT found at treatment termination, was confirmed at 9-months follow-up. German Clinical Trials Register identifier: DRKS00005578..