Background: Although there are effective treatments for posttraumatic stress disorder (PTSD), there is little research on treatments with non-cognitive-behavioural backgrounds, such as gestalt therapy. We tested an integrative gestalt-derived intervention, dialogical exposure therapy (DET), against an established cognitive-behavioural treatment (cognitive processing therapy, CPT) for possible differential effects in terms of symptomatic outcome and drop-out rates. Methods: We randomized 141 treatment-seeking individuals with a diagnosis of PTSD to receive either DET or CPT. Therapy length in both treatments was flexible with a maximum duration of 24 sessions. Results: Dropout rates were 12.2% in DET and 14.9% in CPT. Patients in both conditions achieved significant and large reductions in PTSD symptoms (Impact of Event Scale - Revised; Hedges' g = 1.14 for DET and d = 1.57 for CPT) which were largely stable at the 6-month follow-up. At the posttreatment assessment, CPT performed statistically better than DET on symptom and cognition measures. For several outcome measures, younger patients profited better from CPT than older ones, while there was no age effect for DET. Conclusions: Our results indicate that DET merits further research and may be an alternative to established treatments for PTSD. It remains to be seen whether DET confers advantages in areas of functioning beyond PTSD symptoms.