The objective of this study was to determine the frequency of prenatally diagnosed unilateral cerebral ventriculomegaly and also to assess neonatal outcome in infants with this prenatal diagnosis. A computerized ultrasonography database identified fetuses with isolated and nonisolated unilateral cerebral ventriculomegaly from October 1994 to June 1999. The Denver II Developmental Screening Test was used to assess developmental skills. Unilateral cerebral ventriculomegaly was diagnosed in 15 of 21,172 (1 per 1,411) pregnancies. The width of the enlarged lateral ventricle ranged from 1.0 to 1.9 cm. In 10 (67%) of 15 cases unilateral cerebral ventriculomegaly was an isolated finding. Eight of the 14 infants who were born at 36 weeks' gestation or later had postnatal cranial imaging, and ventricular asymmetry was confirmed in 5 (63%). One infant with an arachnoid cyst and cerebral palsy died at 2 years of age. The remaining 11 infants in whom developmental milestones were assessed had age-appropriate skills. Unilateral fetal ventriculomegaly is usually an isolated finding and when isolated has little measurable effect on developmental outcome.