This study investigated, firstly, the rate of posttraumatic stress disorder (PTSD) and the level of psychological well-being amongst people with chronic fatigue syndrome (CFS); and secondly, the extent to which illness cognitions, defence styles and PTSD symptom severity related to fatigue severity and psychological well-being. Seventy-eight participants with a diagnosis of CFS completed the Chalder Fatigue Scale, the General Health Questionnaire-28, the Posttraumatic Stress Diagnostic Scale, the Illness Cognition Questionnaire and the Defence Style Questionnaire. Fifty-nine participants were recruited from the general public to form the non-fatigued control group. CFS participants had significantly higher levels of PTSD symptoms, lower levels of psychological well-being and more traumatic life events compared to the non-fatigued controls. Trauma exposure and PTSD severity both predicted CFS status. However, regression analyses demonstrated no significant relationship between PTSD symptoms and fatigue severity or the degree of psychological well-being. 'Helplessness' predicted both physical and mental fatigue and psychological well-being, whilst the 'mature' defence styles predicted fatigue severity only. The results offer support to previous research showing that the rate of traumatic life events and PTSD are significantly higher amongst the CFS population. The lack of relationship between PTSD symptoms and fatigue severity or psychological well-being indicates that these processes may operate independently of one another, via different appraisal processes. This study focused on fatigue severity, but it may be that the role of pain in CFS is a key element in the previously reported association between PTSD and CFS. © 2011 Elsevier Ireland Ltd.