One hundred fifty years since Thomas Addison's original description of the disease, it is not commonly appreciated that patients with Addison's disease may present with psychiatric symptoms. A review of the literature indicates that disturbances in mood, motivation, and behavior are associated with Addison's disease. Psychosis occurs less frequently, but can be the presenting symptom of a life-threatening adrenal crisis. Potential mechanisms for the neuropsychiatric symptoms of Addison's disease include electrophysiological, electrolyte and metabolic abnormalities, glucocorticoid deficiency, increased endorphins, and an associated Hashimoto encephalopathy. Physicians must be aware that Addison's disease may present solely with psychiatric symptoms and maintain a high index of suspicion for this potentially fatal condition.