Feminizing syndromes in men are rare and may be related to several causes that usually produce increases in estrogen and androgen secretions. When a feminizing syndrome is caused by an adrenocortical tumor, this is nearly always a carcinoma. The authors report a very rare case of a 59-year-old man with bilateral gynecomastia as the sole presenting symptom of a pure estrogen-secreting adrenocortical adenoma. A presumptive diagnosis was reached by means of a high level of 17B-estradiol, contrast-enhanced computed tomographic (CT) scans, and I-131-norcholesterol scintigraphy and was confirmed pathologically. To the authors' knowledge, there are no other reports of the scintigraphic features of this disorder.