A 20-year-old white female with hirsutism, oligomenorrhea and ovarian enlargement was studied using differential stimulation and suppression of adrenal cortex and ovaries. Although baseline urinary 17-ketosteroid levels were elevated, the patient exhibited normal adrenocortical suppression and stimulation and no increase in urinary 17-ketosteroids during the administration of dexamethasone combined with HCG. At laparotomy a benign cystic teratoma involving the entire left ovary was found. The right ovary had a characteristic polycystic appearance. A left oophorectomy and wedge resection of the right ovary were performed. Cyclic menses with biphasic temperature curves occurred for the first time after surgery, and pregnancy was established in 8 months. The patient's atypical response to dexamethasone and HCG and the possible role of the teratoma in the pathophysiology of her hirsutism are discussed.