Sixty male patients with marked coronal narrowing of the intrathoracic trachea (saber-sheath configuration) were compared with 60 controls. Scores were assigned to patients according to separate clinical and radiographic indexes of chronic obstructive pulmonary disease (COPD). Of the 60 patients with the saber-sheath configuration, 57 (95%) had clinical evidence of COPD compared to only 18% in the control group. Of these 57, 26 (45%) lacked conventional radiographic evidence of COPD. This study establishes a strong correlation between saber-sheath trachea and clinical COPD. The value of this radiographic sign is twofold: (1) as an aid in diagnosing COPD when other convincing radiographic evidence is lacking; and (2) to avoid an erroneous assumption that coronal narrowing is due to a mediastinal mass.