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BACKGROUND The diagnostic threshold for mild autonomous cortisol secretion using low dose, overnight, dexamethasone suppression testing is recognized widely as a serum cortisol ≥1.8 mcg/dL. The degree to which these patients require postoperative glucocorticoid replacement is unknown. METHODS We reviewed adult patients with corticotropin (ACTH)-independent hypercortisolism who underwent unilateral laparoscopic adrenalectomy for benign disease with a dexamethasone suppression testing ≥1.8 mcg/dL at our institution from 1996 to 2018. Patients with a dexamethasone suppression testing of 1.8 to 5 mcg/dL were compared with those with a dexamethasone suppression testing >5 mcg/dL. RESULTS We compared 68 patients with a preoperative dexamethasone suppression testing of 1.8 to 5 mcg/dL to 53 patients with a preoperative dexamethasone suppression testing >5 mcg/dL. Preoperative serum ACTH (mean 10.0 vs 9.2 pg/mL), adenoma size (mean 3.4 vs 3.5 cm), and side of adrenalectomy (37 and 47% right) were similar between groups (P > .05 each). Patients with a dexamethasone suppression testing 1.8 to 5 mcg/dL were older (mean values 58 ± 11 vs 52 ± 16 years ; P = .01), less likely to be female (63 vs 81%; P = .03), had greater body mass indexes (33.1 ± 8.4 vs 29.1 ± 5.6; P = .01), and had lesser 24 hour preoperative urine cortisol excretions (32.6 ± 26.7 vs 76.1 ± 129.4 mcg; P = .03). Postoperative serum cortisol levels were compared in 22 patients with a dexamethasone suppression testing of 1.8 to 5 mcg/dL to 14 patients with a dexamethasone suppression testing >5 mcg/dL. Those with dexamethasone suppression testing 1.8 to 5 mcg/dL had greater postoperative serum cortisol levels (8.0 ± 5.7 vs 5.0 ± 2.6 mcg/dL; P = .03), were less likely to be discharged on glucocorticoid replacement (59% vs 89%; P = .003), and had a decreased duration of treatment (4.4 ± 3.8 vs 10.7 ± 18.0 months; P = .04). CONCLUSION Assessment of early postoperative adrenal function with mild autonomous cortisol secretion is necessary to minimize unnecessary glucocorticoid replacement.