We identified 59 fetuses and infants with intracranial anomalies over 5 1/2 years. The cases represented heterogeneous diagnostic groups: hydrocephalus with a neural tube defect, hydrocephalus with a specified structural anomaly, hydrocephalus of unspecified or miscellaneous cause, holoprosencephaly, and hydranencephaly. One or more major nonneural tube malformations were present in 19 of 54 cases. Eight of 32 cases had a significant chromosomal abnormality. The rate of survival was poor: 13 of 59 pregnancies were terminated electively before 24 weeks gestation, 10 of 59 infants were stillborn, and 16 of the remaining 38 liveborn infants have died since birth. A prenatal ultrasonographic diagnosis was made in the majority of cases (50 of 59). Diagnostic accuracy of prenatal ultrasound examinations ranged from a high of 90% for hydrocephalus to 33% for holoprosencephaly and hydranencephaly, and a low of 22% for the presence of extracranial malformations. Eleven cases in this series could have been considered potential candidates for in utero treatment of ventriculomegaly; this therapy would have been ineffective or inappropriate in eight of these. We recommend that each case undergo thorough diagnostic evaluation, including ultrasound examination and chromosome studies; that parents be informed of the high frequency of associated anomalies, the poor prognosis regarding survival, and the current limitations of ultrasound diagnostic accuracy; and that in utero treatment of fetal ventriculomegaly seems inadvisable at the present time.