Adrenal steroids, particularly glucocorticoids, are used in a variety of conditions ranging from adrenal insufficiency requiring substitution therapy (glucocorticoids and mineral-corticoids), to a wide range of clinical disorders in which undesired inflammatory reactions must be reduced (glucocorticoids). The anti-inflammatory effect, typical of glucocorticoids, is mainly due to the interference with arachidonic acid metabolism, from which both prostaglandins and leukotriens, mediators of inflammation, take origin. ACTH is also employed with the same indications of glucocorticoids, but its use is limited, since its effect depends on the stimulation of cortico-adrenal gland with subsequent release of not only glucocorticoids but also mineral-corticoids and androgens. The therapeutical indications of glucocorticoids are numerous, but dose and duration of treatment vary in relation of the disease that is to be cured. The widespread use of steroids is accompanied by numerous unwanted reactions which depend on their metabolic actions. Therefore corticosteroids must be reserved to well defined clinical conditions and their use should be guided by criteria that are now codified. In this review the physiological and pharmacological effects and the clinical use of corticosteroids have been examined.