One hundred children ranging in age from 1 day to 5 years were examined with an echoencephalographic method especially developed for evaluating ventricular size. All results were related to the diameter of the head and expressed as indices. A midline echo was recorded in all children. More than 3% deviation of this echo from the geometrical midline is considered abnormal. The lateral ventricle index was higher in the newborn infants than in the older children. The echoencephalographic method is rarely suitable for determining the exact width of the lateral ventricles in children 2 years of age or older; only when the ventricles are dilated, as in hydrocephalus, will the method yield reliable measurements.