A 15-year-old girl who presented with primary amenorrhea and virilization had an adrenocortical adenoma that secreted predominantly testosterone. To our knowledge, she is the first peripubertal and second youngest patient with a testosterone-secreting adrenal tumor described. Serum dehydroepiandrosterone sulfate and urinary 17-ketosteroid and 17-hydroxycorticosteroid levels were normal. A tumor was located by a computed tomographic (CT) scan and by uptake of 6-beta-[75Se] selenomethylnorcholesterol. Microscopic examination of the tumor showed typical features of an adrenocortical adenoma with no histologic features characteristic of Leydig cells. Postoperatively, her hirsutism regressed, she rapidly went through puberty, and regular monthly menstruation started four months later. Finding the source of testosterone in a virilized patient can be difficult. Eleven of the 14 previously described patients with testosterone-secreting adrenal tumors initially underwent misdirected surgery on the ovaries. Review of these cases revealed that results of hormone stimulation and suppression tests are unreliable and that these tumors are usually large. Therefore, CT scanning of the adrenal glands is recommended in all patients suspected of having a testosterone-secreting tumor. If the adrenal glands on CT scan are normal, then surgery directed at the ovaries can be undertaken. Adrenal and ovarian vein catheterization is rarely necessary.