On pneumoencephalograms (PEG) of children, assessed as normal, the Evans [See figure in the PDF file] ratio proved to be independent of age, while the septum caudate (S-C) distance showed a slight increase. In assessing the size of the lateral ventricles of children we, therefore, prefer using Evans' ratio. Our knowledge of normal ventricular size in infants under 1 year of age has proved insufficient. Whether the position of the head during the exposure influences the value of the septum caudate distance is discussed.