PurposeTo evaluate the long-term effect of unilateral adrenalectomy (uADX) on patients with primary bilateral macronodular adrenal hyperplasia (PBMAH).MethodsWe retrospectively reviewed 29 patients (including 11 men and 18 women) with PBMAH and Cushing’s syndrome (CS) between 2005 and 2019 who underwent uADX in our center. Clinical symptoms, serum cortisol (8:00 a.m., 4:00 p.m., and 0:00 a.m.), 24 h urinary free cortisol (UFC), computed tomography (CT) scan of the adrenal gland, and pituitary nuclear magnetic resonance (MR) scan performed before and after operation were analyzed.ResultsThe median follow-up time was 39 (13–134) months. uADX decreased significantly at 24 h UFC (median: 357.14 vs. 89.50 ug/24 h,P< 0.001) and serum cortisol (8:00 a.m.) (median: 22.88 vs. 12.50 ug/uL,P< 0.001) 1 year after surgery. In total, 17 of 29 patients had normal UFC again 1 year after surgery, while one of them suffered a relapse after 61 months. However, uADX failed to decrease UFC to the normal range in the other patients. Ten of the remaining 12 uncured patients and the relapsed patient finally underwent contralateral adrenalectomy (cADX). The 24 h UFC of the patients who were cured (n= 17) after uADX was significantly lower than that of the uncured patients (n= 12) (222.30 vs. 579.10 ug/24 h,P= 0.011).ConclusionuADX may be an appropriate treatment for patients with mildly elevated cortisol, while contralateral adrenalectomy (cADX) may be required for patients with highly elevated cortisol. The level of 24 h UFC is helpful to predict patients’ prognosis.