Dysregulations of the hypothalamus-pituitary-adrenal (HPA) axis have been discussed as a physiological substrate of chronic pain and fatigue. The aim of the study was to investigate possible dysregulations of the HPA axis in chronic whiplash-associated disorder (WAD). In 20 patients with chronic WAD and 20 healthy controls, awakening cortisol responses as well as a short circadian free cortisol profile were assessed before and after administration of 0.5mg dexamethasone. In comparison to the controls, chronic WAD patients had attenuated cortisol responses to awakening, normal cortisol levels during the day, and showed enhanced and prolonged suppression of cortisol after the administration of 0.5mg dexamethasone. Dysregulations of the HPA axis in terms of reduced reactivity and enhanced negative feedback suppression exist in chronic WAD. The observed endocrine abnormalities could serve as a systemic mechanism of symptoms experienced by chronic WAD patients.