The human CRH test (hCRH test) is used to differentiate Cushing's disease (CD) from ectopic ACTH secretion (EAS); to assess autonomous cortisol secretion by the adrenal glands; to characterize pseudo-Cushing's syndrome (CS) or adrenal insufficiency (AI).We measured ACTH and cortisol levels; we collected the peak values (peak ACTH and peak cortisol), and calculated the percentage increases (∆% ACTH and ∆% cortisol) after an iv. bolus of 100 μg hCRH.cross-sectional study of using hCRH tests from 2010 to 2019.Referral University-Hospital center.We enrolled 200 patients: 86 CD, 15 EAS, 18 adrenal CS, 25 mild adrenal autonomous cortisol secretion, 31 pseudo-CS, 25 suspected AI.to assess the diagnostic accuracy of hCRH test.The hCRH test was performed mainly for the differential diagnosis of ACTH-dependent CS or adrenal lesions (p=0.048). Peak ACTH and peak cortisol were higher in CD, and ∆% ACTH and ∆% cortisol were able to differentiate CD from EAS with a sensitivity and specificity >80%. In patients with low (<10 pg/mL) or indeterminate (10-20 pg/mL) basal ACTH levels, an absent or reduced peak ACTH response was able to differentiate adrenal from ACTH-dependent forms. Peak ACTH and peak cortisol after hCRH test were lower in pseudo-CS than in CD, but ∆% ACTH and ∆% cortisol were similar. The role of hCRH test in patients with AI was limited.The hCRH test test is the mainstay of the differential diagnosis of ACTH-dependent CS. It is also useful for pointing to a diagnosis of CD in the event of bilateral adrenal masses, and in patients with low basal ACTH.