Six serial ultrasound scans were performed on each of 12 healthy term babies on days 1, 3, 5, 11, 21, and 42 of extrauterine life in order to determine normal neonatal values for various adrenal parameters. Measurements were made of transverse and anteroposterior diameters, of circumference and area in the transverse plane, and of longitudinal length of the adrenals and kidneys. There was a significant decrease in all adrenal parameters of 22%, 25%, 25%, 44%, and 34%, respectively, between days 1 and 5 (p less than .002) and of 46%, 39%, 46%, 67%, and 55%, respectively, between days 1 and 42 (p less than .00005), whereas the kidneys increased in size over the same period.