The purpose of this study is to determine the characteristics of spirometric performance in a group of smokers and to carry out a prospective study of the changes in ventilatory lung function after smoking withdrawal. The ventilatory lung function was studied in 90 smokers and 30 non-smokers. Afterwards the smokers were included in smoking withdrawal program. One year later, the ventilatory function tests were repeated in those individuals who were able to stop smoking. Respiratory function tests were likewise repeated in 10 subjects chosen randomly among those who were not able to stop smoking. The initial study of the ventilatory lung function showed that smokers had significantly lower values of FVC (p < 0.001), FEV1 (p < 0.001), FEVC1/FVC (p < 0.001), FEF25-75 (p < 0.01 and PEF (p < 0.01) compared to non-smokers. Likewise smokers also had a statistically significant higher prevalence rate of obstructive pulmonary disease (p < 0.001). Ventilatory function studies performed one year after smoking withdrawal on those who were able to stop smoking showed a significant improvement of respiratory function parameters compared to studies done one year before. There was also a significant decrease in the prevalence and severity of obstructive pulmonary disease. No differences were observed in the ventilatory function tests performed on the ten subjects who did not stop smoking. From these data we suggest that tobacco consumption produces obstruction of the airways that can be reverted, at least in part, after smoking withdrawal.