Primary adrenocortical insufficiency, or Addison's disease (AD), results from an adrenal cortex hypofunction/dysfunction with a deficient production of glucocorticoids, mineralocorticoids and androgens, and with high levels of both ACTH and plasma renin activity. The prevalence of AD is 110-144 cases per million population in the developed countries. Autoimmune AD is the most frequent etiological form in adult patients, accounting for about 80% of cases, followed by post-tuberculosis AD in 10-15%, the remaining 5% being cases are due to vascular, neoplastic or rare genetic forms. Congenital adrenal hyperplasia is the most frequent form of AD in children and accounts for 72% of cases, whereas autoimmune AD is seen in around 10-15% of cases. The markers of autoimmune AD are adrenal cortex (ACA) or 21-hydroxylase autoantibodies (21-OHAbs) and they are present at diagnosis in more than 90% of cases. In autoimmune AD, the adrenal cortex is infiltrated by lymphocytes and plasma cells and the glands are sclerotic and reduced in volume. Autoimmune AD occurs mainly in middle-aged females, alone or associated with other (clinical, subclinical or potential) autoimmune diseases, giving rise to various forms of autoimmune polyglandular syndrome (type 1, 2 or 4). Replacement therapy with gluco-and mineralocorticoids is life-saving for patients with chronic adrenal insufficiency.