BACKGROUND: Case-finding of chronic obstructive pulmonary disease (COPD) using spirometry may deter people with normal lung function from stopping smoking. The objective of this study was to observe the percentage of smokers screened with normal lung function that quit smoking. METHODS: As part of a study on early detection of COPD, 518 smokers were screened with normal lung function (post-bronchodilator FEV(1)/FVC ≥ 70%). They were invited for a follow-up measurement after an average of 2.4 years. Non-smoking was validated by carbon monoxide ( 0.05 for all comparisons). The average decline in post-bronchodilator FEV(1) was 26 mL/year, which was unrelated to smoking status at follow-up. Non-smokers showed a clinically meaningful and statistically significant (p