Cushing’s syndrome (CS) refers to clinical signs associated with excessive glucocorticoid exposure, including polyuria, polydipsia, polyphagia, and panting. It can be caused by endogenous oversecretion of cortisol or by exogenous administration of glucocorticoids (iatrogenic etiology). Naturally occurring CS can be adrenocorticotropic hormone (ACTH) dependent (85%) or ACTH independent (15%). The vast majority of cases of ACTH-dependent CS are caused by a pituitary tumor (pituitary-dependent hypercortisolism, PDH), and most cases of ACTH-independent CS are caused by adrenal tumors (adrenal-dependent hypercortisolism, or ADH). Other causes, including ectopic ACTH secretion and food-dependent hypercortisolism, will not be discussed here.