In the overwhelming majority of patients, Cushing’s syndrome is caused by an ACTH-producing corticotrope adenoma of the pitu- itary , as initially described by Harvey Cushing in 1912. Cushing’s disease more frequently affects women, with the exception of prepubertal cases, where it is more common in boys. By contrast, ectopic ACTH syndrome is more frequently identified in men. Only 10% of patients with Cushing’s syndrome have a primary, adrenal cause of their disease (e.g., autonomous cortisol excess independent of ACTH), and most of these patients are women. However, overall, the medical use of glucocorticoids for immunosuppression, or for the treatment of inflammatory disorders, is the most common cause of Cushing’s syndrome.