The relationship between smoking, lung cancer and airflow obstruction is recognised but it is unclear whether the presence of minimal lung function damage constitutes an independent risk factor for the development of lung cancer. In order to identify those individuals at higher risk of lung cancer on the basis of functional impairment, we evaluated baseline pulmonary function tests of 3,806 heavy smokers undergoing annual chest computed tomography screening, and compared the forced expiratory volume in 1 s (FEV(1)) % predicted of 57 lung cancer cases and that of 3,749 subjects without cancer. We obtained odds ratios (ORs) of lung cancer and the corresponding 95% confidence intervals (CIs) using unconditional logistic regression, adjusting for age, sex, study and smoking variables. Compared with subjects with FEV(1) >or=90% pred, the OR of lung cancer was 2.45 (95% CI 1.39-4.33) for subjects with FEV(1) <90% pred and 2.90 (95% CI 1.34-6.27) for subjects with FEV(1) <70% pred. These data show that even a relatively small reduction in FEV(1) % pred is a significant predictor of increased lung cancer risk. Test screening for lung cancer using airflow obstruction with FEV(1) <90% is a strategy worth future consideration.