We report herein the case of a 1-year-old boy with McCune-Albright syndrome (MAS) who presented with infantile-onset Cushing' s syndrome caused by ACTH independent macronodular adrenal hyperplasia (AIMAH). Abdominal CT, MRI, and adrenal scintigraphy with (131)I-adosterol identified bilateral adrenal involvement with the left adrenal gland being larger and functionally more active. Unilateral adrenalectomy of the left gland was performed and ameliorated many clinical symptoms, such as Cushingoid appearance and height restriction, and it also normalized many endocrinological data, such as diurnal rhythms of ACTH and cortisol, ACTH and cortisol responses to CRH, and urinary 24 hr free cortisol. Glucocorticoid was replaced for the first 1 year and 6 months after the operation. One adrenal crisis episode occurred at 3 weeks after the operation, but none have occurred since. These results suggest that unilateral adrenalectomy of the larger gland can be an alternative therapy for infantile onset Cushing' s syndrome caused by AIMAH with MAS, when asymmetric involvement is evident and the smaller gland is not markedly enlarged.