Background-The influence of cigarette smoking on the pathogenesis of asthma in the elderly remains controversial. This study attempts to estimate longitudinal changes in HRCT (high resolution computed tomography) parameters and pulmonary function parameters obtained for ex-smokers and never-smokers in asthmatics during 4-yr follow-up period. Methods-Fourteen asthmatics (6 ex-smokers and 8 never-smokers) were studied to determine the influence of aging and cigarette smoking on pulmonary function, and mean lung density (MLD) and the relative area of the lung showing attenuation values less than -950 HU (RA950) on HRCT scans. Results-The values of FVC and FEV1, were significantly more decreased in asthmatics without a smoking history during 4-yr follow-up period. The values of FVC, FEV1, FEV1/FVC and DLco/VA were significantly decreased and RV/TLC were significantly increased in asthmatics with a smoking history over 4 years, and annual decline in FEV1 ex-smokers was larger than that in never-smokers. In the upper lung field, inspiratory MLD was observed to shift in a negative direction and inspiratory RA950 was found to increase during 4-yr observation period in ex-smokers, but not in never-smokers. In the middle lung field, inspiratory RA950 was significantly enhanced in both two groups. Although expiratory MLD, expiratory RA950 and exp RA950/ins RA950 were observed to change significantly during the observation period in ex-smokers, no changes were observed in never-smokers. Conclusion-These results suggest that aging augments airspace enlargement predominantly in the middle lung field, while long term cigarette smoking further worsens emphysematous alterations in the upper lung field.