Aromatase excess syndrome (SIA) is a rare autosomal dominant disease caused by increased extraglandular conversion of androgens to estrogens. SIA is characterizedby early gonadotropin-independent hyperestrogenemia, causing pre-pubertal gynecomastia in boys and premature isosexual development in girls. Adults patients have short stature, due to the early closure of epiphyses because of hyperestrogenemia. Women usually have macromastia, endometrial hyperplastic processes and the late onset of menopause. In men, there is a moderate decrease of gonadotropins, leading to secondary hypogonadism. SIA in children can be suspected on a combination of the clinical picture of an excess of estrogens, increased levels of estrogens with low levels of gonadotropins after the exclusion of an estrogen-producing tumor. The frequency of occurrence of SIA is unknown, due to the rarity of the disease and the complexity of its molecular and genetic verification. In this article, we describe a clinical case of a 10-year-old patient with a late diagnosis of aromatase overactivity syndrome caused by a 15q21.2 microduplication of the CYP19A1 gene, and conduct a brief review of the literature.