Addison’s disease is primary adrenocortical failure. Thomas Addison first described the disease in a group of patients who died from severe anaemia with diseased adrenal glands in 1855. At this time, most cases described were caused by tuberculosis affecting the adrenal glands, though the most common cause now is autoimmune destruction. It remains a rare disease, with an incidence in the Western world of 40–60/million and a prevalence of 120/million. However, it is important to diagnose the condition promptly to prevent patients presenting with a life-threatening crisis. The most common symptoms are nonspecific, such as fatigue, nausea, anorexia and weight loss, and therefore diagnosis is often delayed. In developed countries, 75–80% of cases of Addison’s disease are caused by autoimmunity; tuberculosis is the second most common cause. Patients are often hyponatraemic and hyperkalaemic at presentation. After clinical suspicion is aroused, the diagnosis is confirmed by serum cortisol and plasma adrenocorticotrophic hormone measurements. The aim of treatment is to restore the deficient hormones, usually with hydrocortisone and fludrocortisone, and treat the underlying cause if possible.