In an effort to establish normal values for both investigational and patient care purposes, computed tomography was used to determine the length, diameters, cross-sectional area, and volume of the tracheas of 34 children up to the age of 6 years. The measurements were taken when patients were asleep or resting quietly during tidal breathing, at perhaps 30-60% of total lung capacity. The results were related to body height (in infancy, to body length). There was virtually no difference between boys and girls. Each mean diameter correlated well with mean cross-sectional area. Tracheal diameters and area were reasonably constant over the length of individual tracheas. The slopes of the functions relating height to tracheal dimensions in these 34 infants and young children were slightly less steep than those previously measured near total lung capacity in 90 older children and adolescents.