Steroid cell tumors are rare. Only 23 cases have been described to date, most of then causing inappropriate virilization in girls. We present here the second case in literature of isosexual pseudoprecocious puberty due to a steroid cell tumor in a girl who came to our Service with a probable diagnosis of true precocious puberty. The child presented bilateral breast development at 2 ys. of age, increased growth velocity and pubarche; she had been treated with cyproterone at another clinic. Physical examination- CA: 3 ys-old, Height: 106 cm (+2.3 SD); Bone Age: 5 y-old; breasts and pubic hair Tanner Stage III; Clitons: 0.8 cm. Ultrasonography and C.T. Scan of the abdomen and pelvis disclosed a 4 cm tumor in the right ovary. Laboratory evaluation showed elevated E2. 96 pg/ml, Aldosterone: 35 ng/dl and DHEAS: 1142 ng/ml; slightly elevated testosterone, 17-OHP, DHEA, androstenedione and S-Compound. Basal LH and FSH could not be detected by immunofluorimetric method as well as after GnRH stimulation All other laboratory analyses were normal. The child underwent a right ooforectomy and the anatomo-pathological examination showed a steroid cell tumor with morphologic pattern consistent with the zona glomerulosa of the adrenal cortex. After surgery the child had regression of breast development and all laboratory measurements became normal. This case discloses that steroid cell tumor are rare causes of isosexual pseudoprecocius puberty and may present with the clinical feature of true precoucious puberty.