AIM Fetal borderline ventriculomegaly represents a frequent dilemma in perinatal management. The present study aimed to evaluate the clinical significance of fetal borderline ventriculomegaly in a low-risk Japanese population and to identify the risk factors for associated anomalies. METHODS Data of cases of fetal borderline ventriculomegaly detected at 26-28 weeks of gestation by routine ultrasonographic screening of low-risk singleton pregnancies between 2006 and 2012 were retrospectively collected. Ventricular width, in utero progression, associated anomalies, chromosomal abnormalities, and perinatal and postnatal outcomes were assessed. The ventricular width, in utero progression and other perinatal characteristics were compared between the isolated and non-isolated groups. RESULTS Among the total 6020 singleton low-risk pregnancies, we noted that 42 had borderline ventriculomegaly. Six (14%) of these cases had other defects by subsequent detailed examination. Ventriculomegaly resolved or regressed in 35 (83%) and progressed in four (10%) cases, of which three were associated with other anomalies. The median ventricular width was 12.8 mm (range, 10.0-14.7) in the six non-isolated cases and 10.5 mm (range, 10.0-13.3) in the 36 isolated cases; the differences were statistically significant. A ventricular width of 12 mm or more and in utero progression were more frequently observed in non-isolated cases than in isolated cases. CONCLUSION Fetal borderline ventriculomegaly frequently resolves in utero. A ventricular diameter of more than 12 mm and in utero progression are risk factors for additional anomalies. After the initial diagnosis of borderline ventriculomegaly, the pregnancy should be carefully followed up to determine whether the ventricle size is resolved, remains stable or increases.