ABSTRACT Background: Literature on the association between therapist adherence and treatment success in the treatment of post-traumatic stress disorder (PTSD) is scarce, and the results are mixed. Objective: To examine the relationship between therapist adherence to dialectical behaviour therapy for PTSD (DBT-PTSD) and cognitive processing therapy (CPT) on treatment outcome in women with PTSD and emotion regulation difficulties after interpersonal childhood abuse. Method: Videotaped therapy sessions from 160 female participants of a large randomized controlled trial [Bohus, M., Kleindienst, N., Hahn, C., Müller-Engelmann, M., Ludäscher, P., Steil, R., Fydrich, T., Kuehner, C., Resick, P. A., Stiglmayr, C., Schmahl, C., & Priebe, K. (2020). Dialectical behavior therapy for posttraumatic stress disorder (DBT-PTSD) compared with cognitive processing therapy (CPT) in complex presentations of PTSD in women survivors of childhood abuse. JAMA Psychiatry, 77(12), 1235. jamapsychiatry.2020.2148] were rated. Adherence to CPT and DBT-PTSD was assessed using two specifically developed rating scales. Results: Higher therapist adherence was associated with a greater reduction of clinician-rated PTSD symptom severity. This effect was more pronounced in the CPT group than in the DBT-PTSD group. Adherence was also related to a greater reduction of self-rated PTSD symptoms, borderline symptoms, and dissociation intensity. Conclusion: Our results indicate that higher therapist adherence can lead to better treatment outcomes in PTSD treatments, especially in CPT.