Using computed tomography, we measured the tracheas of 100 subjects younger than 20 yr of age. The 10 youngest were sleeping. The other 90 were awake, and most were measured near total lung capacity. Tracheal length, mean anteroposterior diameter, mean transverse diameter, mean cross-sectional area, and contained volume were plotted against body height for all 100 subjects. The relationships of these dimensions to body height were derived for the 90 subjects examined awake. The resulting regressions had r values of 0.88 to 0.92. The exponents for height were 1.22 to 1.37 for the linear dimensions, 2.58 for area, and 3.80 for volume. We found no differences between the sexes. Variability in diameters and area along individual tracheas was small, especially after early childhood. Such variability as occurred tended to preserve shape slightly more than size. This constancy allows accurate prediction of tracheal area from either tracheal diameter.