Prenatal diagnosis of congenital adrenal hyperplasia (CAH) by direct mutation detection in previously genotyped families from the aspects of CAH permits prenatal treatment of affected females. This spares the affected female the consequences of genital ambiguity, genital surgery, possible sex misassignment, and gender confusion. Here, we present a homozygous affected female fetus. The family also has a son affected by salt-losing type CAH. Genetic mutation analyses of 21-hydroxylase gene (CYP21A2) in the parents and their son were performed previously from the second pregnancy. Parents and their son (index case) harbored a Q318X mutation in the CYP21 gene encoding the steroid 21-hydroxylase enzyme. Dexamethasone was introduced at the sixth week of the second gestation. After 10 completed weeks, a chorionic villus sampling (CVS) was taken, followed by sex typing and CYP21A2 genotyping. The affected female fetus with the same mutation was confirmed and dexamethasone treatment was continued until term. A significant increase in weight gain and blood pressure was observed during the pregnancy. At the 34th week of gestation, a small gestational age (SGA) female baby with normal female genitalia was delivered. The diagnosis was confirmed postnatally by mutation analysis using peripheral blood sampling. The molecular study performed in this family allowed us to give prenatal treatment and to avoid the genital virilization of external genitalia of the affected female fetus. The medical treatment of CAH before birth is a rare example of the successful prevention of a major congenital malformation. However, there is still a need to collect more data concerning possible rare unfavorable effects of this therapy. Long-term follow-up of the safety of prenatal treatment is currently underway. To the best of our knowledge, this is the first reported Turkish case of prenatally diagnosed and treated Anahtar Kelimeler : konjenital adrenal hiperplazi, prenatal tanı ve tedavi