This case report describes a 53-year old man with Cushing's syndrome due to Adrenocorticotropic Hormone (ACTH) independent bilateral adrenocortical macronodular hyperplasia (AIMAH). His plasma cortisol showed no diurnal rhythm and was unsuppressable by high-dose dexamethasone. Plasma ACTH was undetectable and did not respond to corticotrophin-releasing hormone. The aetiology of this rare disease remains uncertain. The treatment is based on bilateral adrenalectomy.