Although trauma-focused cognitive behavioral therapy (TF-CBT) with exposure is an effective treatment for posttraumatic stress disorder (PTSD), not all patients recover. Addition of breathing biofeedback to exposure in TF-CBT is suggested as a promising complementary technique to improve recovery of PTSD symptoms. Patients (n = 8) with chronic PTSD were randomized to regular TF-CBT or TF-CBT with complementary breathing biofeedback to exposure. PTSD symptoms were measured before, during and after TF-CBT with the Impact of Event Scale-Revised. The results show that breathing biofeedback is feasible and can easily be complemented to TF-CBT. Although PTSD symptoms significantly decreased from pre to post treatment in both conditions, there was a clear trend towards a significantly faster (p = .051) symptom reduction in biofeedback compared to regular TF-CBT. The most important limitation was the small sample size. The hastened clinical improvement in the biofeedback condition supports the idea that breathing biofeedback may be an effective complementary component to exposure in PTSD patients. The mechanism of action of breathing biofeedback may relate to competing working memory resources decreasing vividness and emotionality, similar to eye movement desensitization and reprocessing. Future research is needed to examine this.