BACKGROUND: Cortisol secretion in elderly persons with anxiety disorders exposed to common stressful situations has not been evaluated. METHODS: Salivary-free cortisol levels were evaluated at 8, 15, and 22 h, in 201 elderly subjects during stressful and non-stressful days. Psychiatric symptomatology was assessed by a standardized psychiatric examination (MINI). RESULTS: Elderly subjects without psychiatric disorder showed a sustained increase in cortisol secretion several hours after the exposure to a stressful situation. In comparison, subjects with anxiety disorders showed a greater increase in cortisol secretion in the stressful situation, with lowered recuperation capacity. This effect was dose-dependent as a function of anxiety co-morbidity. Persons reporting lifetime major trauma with intrusions exhibited lowered continuous basal cortisol associated with efficient recuperation capacity. Independently of psychopathology, women appeared more reactive to stressful environmental conditions. LIMITATIONS: Exclusion of institutionalized persons and benzodiazepine users may have led to sampling of less severe anxiety symptoms. CONCLUSIONS: Dysregulation of the hypothalamic-pituitary-adrenal axis was observed in elderly persons with anxiety disorders experiencing environmental stress. A common pattern of up-regulated diurnal cortisol secretion was observed in anxious subjects with lifetime and current anxiety disorder irrespective of sub-type (generalized anxiety, phobias) suggesting a stable trait and a common "core" across disorders. Elderly persons who had experienced trauma with subsequent intrusions showed a distinct pattern with down-regulated activity.