Congenital adrenal hyperplasia (CAH) due to steroid 21-hydroxylase deficiency is a common cause of genital virilization in female infants resulting from inappropriate fetal adrenal androgen secretion. Some investigators have advocated treating pregnant women who are at risk for carrying a CAH fetus with dexamethasone to suppress fetal adrenal androgen synthesis. Experience to date shows that this treatment can be effective in ameliorating the genital virilization in female fetuses. However, the doses used are supraphysiological, the mechanism of dexamethasone action in the fetus is unclear and no long-term followup studies have been done. To be effective the treatment would need to be started by week 6 of gestation but the genetic diagnosis cannot be made until week 12. If the mother has had a previous CAH child, only 1 in 4 pregnancies will be affected and only the female fetuses stand to benefit from treatment, thus, 7 of 8 fetuses will be treated needlessly. In view of these and other concerns, the prenatal treatment of CAH remains an experimental therapy and, hence, must only be done with fully informed consent in controlled prospective trials approved by human experimentation committees at centers that see enough of these patients to collect meaningful data.