Congenital adrenal hyperplasia due to 21-hydroxylase deficiency can result in marked virilization of the external genitalia of affected female subjects. Theoretically, suppression of the fetal pituitary-adrenal axis with glucocorticoid during gestational weeks 9 to 17 should prevent the development of ambiguous genitalia in the female fetus. Prenatal diagnosis of congenital adrenal hyperplasia can be made on elevated amniotic fluid 17-hydroxyprogesterone and adrenal androgen concentrations, and HLA typing of cultured amniotic fluid cells. However, these tests cannot be completed before 16 to 17 weeks of gestation, and maternal therapy would have to be instituted before the exact genetic status of the fetus is known. Chorionic villus sampling during the first trimester provides an alternative to second trimester diagnosis in patients who are at risk for bearing offspring with congenital adrenal hyperplasia. We report the use of dexamethasone suppression at 8 weeks of gestation in a 34-year-old woman whose son had congenital adrenal hyperplasia due to severe salt-losing 21-hydroxylase deficiency and whose biopsy revealed a 46XX chromosomal pattern. Cultured cells from the biopsy confirmed the fetus to be of identical HLA haplotype to the previous affected sibling. At 41 weeks the patient delivered a female neonate with minimal prominence of the clitoris, mildly rugated labia, a single perineal opening and minimal posterior labial fusion. Postnatal tapering of maternal steroids was performed with no long-term sequelae.