Aim of this study was to analyze the performance of CRH, desmopressin and high-dose dexamethasone suppression test (HDDST) in the differential diagnosis of ACTH-dependent Cushing’s syndrome as well as the impact of invasive and noninvasive tests on surgical outcome in patients affected by Cushing’s disease (CD). This evidence concerns the gene POMC and Cushing syndrome due to macronodular adrenal hyperplasia.