Abstract Objective: To assess the upper airway (UAW) total volume (TV), the nasopharyngeal narrowest area (NNA), and the oropharyngeal narrowest area (ONA) in patients with bronchial asthma. Materials and Methods: The sample consisted of 52 patients divided into two groups: the control group (n  =  26; mean age  =  14.85 years), which consisted of patients not suffering from bronchial asthma; and the asthmatic group (n  =  26; mean age  =  16.65 years), which consisted of patients with bronchial asthma. To assess UAW-related variables (TV, NNA, and ONA), cone-beam computed tomography scans of the patients were evaluated by means of the Dolphin Imaging software 11.5. All measurements were repeated after 30 days, and the results were submitted to reliability tests by means of the intraclass correlation coefficient and the Bland-Altman agreement test. The values obtained for TV, NNA, and ONA for each group were compared by using Student's t-test for independent samples (5% level of significance). Results: The results showed that the groups were matched concerning gender, cephalometric characteristics, and type of malocclusion. The asthmatic group had significantly lower TV (P  =  .01) and ONA (P  =  .007) than the control group. However, no significant difference was observed for NNA between the groups (P  =  .54). Conclusions: Bronchial asthma may be a determining factor for the reduction of UAW dimensions, as patients with asthma showed significant reductions in TV and ONA dimensions.