Because mechanical properties of central airways play an important role in determining maximal expiratory flow, we examined how tracheal size and maximal expiratory flow changed with age in 50 asymptomatic men, 19 to 61 yr of age, who were lifelong nonsmokers. Cross-sectional area (X-SA) of the intrathoracic trachea was estimated from posteroanterior and lateral chest radiographs taken at full inflation. Maximal expiratory flow-volume curves and spirometry were measured by standard techniques. Tracheal X-SA averaged 2.81 cm2 (SD, 0.38) at mean age 21.1 yr and 3.22 cm2 (SD,0.41) at mean age 52.5 yr, and correlated with peak expiratory flow (PEF) (r = 0.522, p less than 0.001) and FEV1 (r = 0.437, p = less than 0.01) (both expressed as percent predicted values based on age and height). These relationships were weaker than previously described in young men. The results suggest that with increasing age, large airways lose elastic recoil, as previously described for the air spaces. Aging changes in the airways may offset the unfavorable effects of loss of lung recoil and account for the relatively good preservation of PEF and the lack of rise in airways resistance with increasing age.