A computer method that calculates tracheal cross-sectional area by compensating for partial volume averaging was developed and validated in a study with phantoms. The program was then used to determine the tracheal cross-sectional area of 30 normal children who ranged in age from four months to 18 years. CT-derived cross sections were correlated with age, height, weight, and body-surface area, and they were compared with findings of published clinical and post-mortem studies. CT cross-sectional areas ranged from 20-275 mm2, varied by as much as 22% at the three different tracheal levels studied, and appeared to correlate most closely with body height. CT-derived tracheal cross-sectional areas are quite similar to those in published reports of postmortem and clinical studies. Measurement of tracheal cross section by CT may prove useful in quantitating tracheal compromise by intrinsic or extrinsic causes.