Posttraumatic Stress Disorder (PTSD) has frequently been found to have an impact on the development of obesity, with the relationship between past traumatic episodes and obesity usually thought of as uni-directional. The purpose of the present study was to examine whether the level of PTSD-symptoms would decrease as a result of weight loss in obese participants during a 16 week stay at a weight loss facility. During the 16 weeks participants’ Body Mass Index (BMI) decreased significantly. Concurrently, a significant decline in the level of PTSD symptoms was also reported. During the first week of treatment, 17 participants (57%) qualified for the diagnosis of PTSD when measured by a standardised checklist for PTSD symptoms. By week 16, only 6 participants (20%) qualified for the PTSD diagnosis. The findings are discussed in terms of cognitive theories of PTSD.