PURPOSE: This study is directed to evaluate standardized developmental test performances of infants and children who, as fetuses, had mild isolated cerebral ventriculomegaly diagnosed by ultrasound. METHODS: All prenatal sonographic findings from 2001 to 2002 were evaluated. Live isolated mild ventriculomegaly (IMVM) of 10-15 mm were observed in 95 cases (1.1 percent). Standardized developmental testing of 40 cases of IMVM and 36 cases in a comparison group were offered to parents Both groups of children were adjusted to normal antepatum subjects with respect to sex, race, indication for ultrasound and gestational age at the time of ultrasound. Test of cognitive and motor development (Bayley Scales of Infant Development, Second Edition; BSID-II) were administered by developmental examiners. RESULTS: Forty cases and 34 comparison sujects completed the testing. The IMVM and comparison groups were similar with respect to parental age, gestational age, birth weight, familial socioeconomic status. The IMVM subjects scored lower than the comparison group on both the BSID-II, but there was not statistically significant. differences; metal development index (MDI) (92.7+/-12.9 vs 94.7+/-14.1, P=0.47) and psychomotor development index (PDI) (100.3+/-14.1 vs 101.3+/-10.7, P=0.75). Eleven cases (27.5 percent) of IMVM group and five cases (14.7 percent) of the comparison group were developmentally delayed, but most cases in both groups showed mild delays. Resolution or lack of progression, lateral ventricle diameter < or= 12 mm and females were associated with better scores, but there were not statistically significant. Polarity, and head circumference were not related to later development. CONCLUSION: This study show children with MIVM did not delay performance in the developmental test, but we might suggest a tendency to increase the risk of mild developmental delay.