This article presents the computed tomographic (CT) features of the most common abnormalities of the trachea and main-stem bronchi and correlates CT and pathologic findings. The abnormalities are classified into focal and diffuse. Focal disease tends to produce a decreased airway diameter, whereas diffuse diseases are divided into those that increase the airway diameter and those that decrease it. Conventional CT with 10-mm collimation was performed in 36 patients to assess their condition. Additional dynamic incremental thin-section (1.5-5.0-mm collimation) CT was performed in patients with focal abnormalities. Findings from conventional CT correlated closely with those from pathologic analysis of specimens from patients with diffuse disease, but dynamic thin-section scans are necessary for optimal assessment of focal abnormalities. CT demonstrates the location and extent of disease; helps characterize abnormal tissues; helps evaluate the thickness of the tracheal and bronchial walls; and helps determine the extent of extraluminal disease, including the presence of mediastinal extension and lymphadenopathy.