Stress influences the whole body, including the gut. Irritable bowel syndrome (IBS) is a syndrome characterized by gastrointestinal symptoms, with the absence of clinical signs. IBS is seen in several psychiatric co-morbidities. Only few studies have examined the association between IBS and posttraumatic stress disorder (PTSD). There are several hypotheses of how this association can be explained, e.g. oxytocin dysregulation, hypothalamic-pituitary-adrenal axis dysfunction, the vulnerability of the patient group, post-infectious irritable bowel and side effects of the medical treatment of PTSD.