Background: Clinicians frequently describe changes in facial affective behavior during the treatment of posttraumatic stress disorder (PTSD). An increase in facial affective behavior is seen in association with a reduction of numbing symptoms. Objective: The purpose of this exploratory study was to demonstrate the changes in facial affective behavior (especially negative affects) during inpatient eye movement desensitization and reprocessing (EMDR) treatment and to examine to what extent these changes correspond to shifts in symptom severity. Material and methods: Facial affective behavior was coded during therapeutic sessions for 16 patients who were chronically traumatized during their youth, using the facial action coding system (FACS) for 3 time points, before, during and 1 year after treatment with EMDR. Data of the impact of event scale revised (IES-R), the symptom checklist (SCL-90-R), Beck depression inventory (BDI-V) and a questionnaire for dissociative symptoms (FDS) was documented for 16 female patients with a mean age of 39 years (SD = ±10). Results and conclusion: There was a significant change in facial affective behavior during and after treatment (Ï2(2) = 5.73, p = 0.030). Total facial affective behavior and the expression of negative affect significantly increased 1 year after therapy; however, there were no significant correlations between the change of facial affective behavior during EMDR treatment and relevant outcome variables. Further research will show if monitoring facial affective behavior is useful to assess therapeutic success, especially with respect to social interactions. © 2017, Springer Medizin Verlag GmbH.