The extent of the cerebrospinal fluid (CSF) spaces was measured in 247 CT examinations, reported as normal, in children aged 3 months to 14 years. The measurements of the CSF compartments were divided by the sum of the transverse and longitudinal internal cranial diameters in the corresponding CT section, in order to take into account the size and shape of the growing skull. All CSF spaces were relatively larger in the younger (< or = 3 years) than in the older children, but did not differ between boys and girls, since the cranial size was taken into account. The CSF compartments increased in a non-uniform manner during the first 3 years of life, but after the age of four they developed uniformly and in parallel with the growing skull. Measurements of the subarachnoid spaces formed an age-related table, which may be of value when interpreting brain CT examinations of children.