A rare case of an adrenal adenoma that produced virilization by an isolated secretion of testosterone without a concomitant increase in 17-ketosteroids is reported. It was erroneously concluded that the patient's hypertestosteronemia was due to an ovarian disorder because the urinary 17-ketosteroids were normal. It then was speculated that the adenoma's enzyme system was so efficient it was capable of converting the more prevalent androstenedione directly to testosterone without metabolizing it to 17-ketosteroids. Removal of the adrenal adenoma completely cured the patient's hirsutism.