Background: Dilated perivascular or Virchow-Robin spaces (VRS) are a common finding in adult brain MRI studies and are generally presumed to have no significance, marking the path of the lenticulostriate arteries. Large series of adults have noted an association with senescence; other studies have not supported this observation and have reported their common presence in children. The single large childhood series reported an association of VRS with developmental delay, psychiatric problems, and headaches. VRS increase in size due to pathologic processes of some conditions, such as mucopolysaccharidoses and cryptococcosis. The frequency and size of VRS in pediatric patients at the level of the anterior commissure as detected by MRI scan has not been studied to our knowledge. Objective: We undertook a retrospective study of pediatric brain MRI to determine the frequency, size, and possible associated diagnoses of dilated VRS in the region of the anterior commissure. Methods: 218 brain MRI studies were reviewed with patients ranging in age from 1 week to 18 years. Scans were scored for presence or absence of VRS at the level of the anterior commissure and were considered positive if the signal intensity of lesions at the appropriate site matched that of CSF on both T1- and T2-weighted images. The VRS were measured for greatest diameter. Diagnoses or clinical complaints which had prompted the scan were recorded. Results: Dilated VRS were absent in 36% of scans and present in 64%, with 40% measuring <3.0 mm, 20% measuring 3.0-5.7 mm and only 4% measuring > 5.7 mm in greatest diameter; none measured larger than 12 mm. VRS were more likely to be present in older patients, but when present, the size of VRS was similar at all ages. No single diagnosis was associated with large VRS in our study. Conclusions: Small VRS are common in pediatric brain MRI but spaces > 5.7 mm appear to be rare. In our series, the size of VRS did not increase with age. No single diagnosis was associated with the presence of large VRS (> 5.7 mm) in this series of patients. Further study regarding the possible clinical significance of large VRS in pediatric brain MRI is warranted.