A girl aged 12 years and 10 months presented with deepening of the voice first noted 7 months earlier. Pubertal development was almost completed. The girl had regular monthly menses and no signs of hirsutism, clitoris enlargement or Cushing’s disease. Serum testosterone was about threefold above normal, whereas dehydroepiandrosterone was in the upper normal range. The 17-ketosteroids as well as the gas-chromatographically analyzed 5α and 5β derivatives of testosterone from urine were slightly increased. Other serum and urinary steroids were normal. Dynamic tests of the endocrine function exhibited inconclusive results. Ultrasonography revealed no ovarian cysts. A small, left-sided adrenal mass was identified by computed axial tomographic scan and removed by surgery. There were no signs of local metastasis nor of vascular extension. The histopathological diagnosis was adrenocortical carcinoma. 5 months after surgery, the preoperatively elevated steroid levels had returned to normal.