Described in this article is the massive enlargement of both adrenal glands in 3 newborns-2 girls and 1 boy. Two had hemihypertrophy and other congenital abnormalities but no identified genetic mutation; the third had genetically proven Beckwith-Wiedemann syndrome. Two had severe Cushing syndrome, the third had hypercortisolemia but no clinical Cushing syndrome. Bilateral adrenalectomy cured Cushing syndrome in the 2 with severe symptoms; total adrenal weight in these patients was 44 and 53 g, respectively. Unilateral adrenalectomy was performed in the third patient: the gland weighed 52 g; postoperatively, the patient's hypercortisolemia normalized, and, concomitantly, the enlarged contralateral adrenal gland had a 5-fold decrease in size with slight enlargement 6 years postoperatively. Microscopically, the 3 patients had similar pathology: massive adrenal enlargement due to a combination of cytomegaly, persistence of the transient cortex, and hyperplasia of the permanent cortex. The pathologic findings were most likely the result of the genetic mutation identified in 1 patient and of an unknown mutation in the remaining 2 patients.