Background; Eating disorder patients with a posttraumatic stress disorder have worse treatment results regarding their eating disorder than patients without a posttraumatic stress disorder. Many underweight eating disorder patients with co-morbid posttraumatic stress disorder symptoms are not treated for their posttraumatic stress disorder symptoms during underweight. We pose that posttraumatic stress disorder treatment in underweight eating disorder is possible, and tested whether posttraumatic stress disorder symptoms decrease with Imagery Rescripting, and secondary whether the treatment of trauma has an effect on the process of weight gain and on eating disorder pathology in general.Method; Ten patients in clinical treatment (BMI 14-16.5) participated. A multiple baseline design was used, with baseline varying from six to 10 weeks, a six-week treatment phase, a three-week follow-up period and a three month follow-up measurement. Data were analyzed with mixed regression. Results; Evidence was found for strong effects of treating posttraumatic stress disorder symptoms with imagery rescripting without interfering with the eating disorder treatment. Positive effects were also found on a range of emotional and cognitive secondary measures.Conclusion;Imagery rescripting of traumatic memories at times of underweight was possible, safe and had positive clinical effects. Trial registrationNetherlands trial register (NTR) Trial NL5906 (NTR6094). Date of registration 09/23/2016. https://www.trialregister.nl/trial/5906