Among fetal anomalies, the rate of the central nervous system (CNS) abnormality is high, and almost all cases are wanted to diagnose prenatally for the improvement of their prognosis. For instance, anencephaly should be detected for its lethal prognosis. Hydrocephalus has a certain possibility for intrauterine treatment. Spina bifida should be found in utero for the immediate operation after birth. At present, most of these major anomalies of CNS can be successfully screened or diagnosed by using ultrasonography. Brain anomalies such as hydrocephalus, Dandy-Walker anomaly and holoprosencephaly show characteristic dilatation of ventricles, which can be easily found in the routine screening ultrasonography from the beginning of the second trimester of gestation. Ultrasonographic detection of neural tube defects such as anencephaly and spina bifida is not difficult in utero. Thus it is possible to diagnose the most of CNS anomalies by using prenatal ultrasound in the early stage of gestation now. Recent advances of ultrasonography, particularly the development of transvaginal technique have contributed to the earlier diagnosis of CNS anomaly even in the first trimester of gestation.