Among 80 women with congenital adrenal hyperplasia due to 21-hydroxylase deficiency (40 with the simple virilizing form and 40 with the salt-losing form), 40 reported having an adequate introitus and being heterosexually active. In 15 of 25 patients with the simple virilizing form, 25 pregnancies resulted in 20 normal children, whereas only 1 of 15 women with the salt-losing form became pregnant; this pregnancy was electively terminated. Several factors seem to be responsible for the low fertility rates: noncompliance with therapy was probably high, as suggested by hirsutism and poor endocrine follow-up in 25 percent of patients; whereas 49 patients had regular menstrual periods, 14 had irregular periods, 10 had amenorrhea, 5 had undergone hysterectomy, and 2 had entered menopause; 87 percent of patients with salt loss and 50 percent of those with simple virilization (P less than 0.001) had remained single; the vaginal introitus was reported to be inadequate for intercourse by 35 percent of patients (53 percent of those with salt loss and 18 percent of those with simple virilization; P less than 0.002); and heterosexual activity was reported less frequently among patients with an inadequate introitus. The status of the introitus seemed to have a more important role in the sexual activity reported than did the degree of prenatal exposure to androgen (which was higher among patients with salt loss than among those with simple virilization). However, our data did not rule out an effect of androgen exposure on female fetuses. Our experience indicates that improved surgical correction of the external genitalia and better compliance with therapy will be necessary to improve fertility rates among women with congenital adrenal hyperplasia due to 21-hydroxylase deficiency.