Recent studies suggest that thoracal high resolution computed tomography (HRCT) of the thorax can detect the irreversible structural changes in chronic asthma cases. This study is aimed to evaluate these possible changes and their relation with asthma severity. Twenty-eight stable asthmatic patients with normal conventional radiography and 10 healthy controls were included. Twenty of the patients were female (71.4%) and the mean age of the group was 43 +/- 10.5 (30-61). The groups were divided into 2; as group 1 included mild intermittent and mild persistent cases, and group 2 included moderate and severe persistent cases. Asthma and control group, and group 1 and 2 were compared according to the thickness of airwall (T), thickness to outer diameter (T/D), wall area (WA), the percentage wall area (WA%). HRCT showed that air trapping, bronchiectasis, fibrotic lesions and airwall thickening were significantly more common in asthma group (p< 0.05). Emphysema, acinar pattern, collapse and mucoid impact were common in asthma group (p> 0.05). The incidence of T and WA was higher in asthma group but also did not reach statistical significance and the thickening of airwall in small airways was significantly more in asthma group. Any correlation between HRCT findings and asthma severity was not found. So reversible and irreversible bronchial and parenchymal changes, detected by HRCT but not by plain chest radiograms, may be present in asthma cases. The early detection of these changes may lead more aggressive asthma management.