Pathological changes of nasosinus occur often in subjects with bronchial asthma. Coexisting nasosinus lesion may affect pathophysiology of lower respiratory tract in asthmatics. The extent of nasal and sinus lesion was quantified in 17 patients with bronchial asthma, and their relationships to atopic status, asthma severity and bronchial hyperresponsiveness were evaluated in this study. Opacification degree of maxillary sinuses and nasal mucosa thickening were quantified using CT scans. The opacification degree was evaluated as (total opacification area)/(total maxillary sinus area). Although the opacification degree of maxillary sinuses in atopic patients showed no significant difference compared with that in non-atopic patients, maximum nasal mucosa thickening in atopic patients had a significant difference compared with that in non-atopic patients (p=0.028). In severe asthmatics, the opacification degree of maxillary sinuses was significantly more prominent compared with those in moderate and mild asthmatics (p=0.0005, p=0.036, respectively). Significantly marked nasal mucosa thickening was recognized in mild asthmatics compared with that in moderate asthmatics (p=0.0462). Regarding bronchial hyperresponsiveness, a significant correlation between Dmin and the opacification degree of maxillary sinuses was observed (rs= -0.551, p=0.0276). Nasal mucosa thickening had no correlation with bronchial hyperresponsiveness. The results suggest that sinusitis may affect bronchial hyperresponsiveness and asthma severity. Treatment of sinusitis may lead to improvement of asthma symptoms.