We report on a case of a 2 2/12-year-old boy with heterosexual precocious puberty secondary to a feminizing adrenocortical adenoma. The boy, with no previous history of disease or treatment, presented with bilateral gynecomastia and pubic hair development (Tanner III breasts and Tanner II pubic hair). Plasma estradiol and testosterone were 410.9 pg/ml and 126.2 ng/dl respectively. Basal plasma LH and FSH levels were within the normal range. Bolus i.v. injection of GnRH showed unresponsiveness of LH and FSH. Abdominal echography and abdominal magnetic resonance imaging revealed a well-defined mass at the left suprarenal region (measuring 4.0 x 2.7 x 3.6 cm in size). After removal of the adrenal tumor, the estradiol and testosterone levels fell to normal in 2 weeks. The gynecomastia and pubic hair regressed with time. The pathology of the tumor showed compact pattern with polygonal cells containing moderate eosinophilic cytoplasm without mitotic figure. These findings were consistent with an adrenocortical adenoma secreting estradiol and testosterone as the cause of the patient's heterosexual precocious puberty.