Adrenocorticotropic hormone (ACTH) independent Cushing syndrome is a form of endogenous Cushing syndrome (CS; see this term) that may result from excess secretion of cortisol by either a unilateral and benign (adrenocortical adenoma: 55-60%) or malignant (adrenocortical carcinoma: 35-40 %) adrenocortical tumor or by bilateral adrenal secretion by macronodular adrenal hyperplasia (AIMAH), as an isolated disease or as part of McCune-Albright syndrome (MAS), or by primary pigmented nodular adrenocortical disease (PPNAD), as an isolated disease or as part of Carney complex (CNC; see these terms).