Systematic screening of COPD allows identification of subjects with persistent airway obstruction who do not complain of any symptom. Little is known about subjects with undiagnosed persistent airway obstruction. We aimed to compare some clinical and spirometric data between subjects with spirometrically-defined COPD (i.e., persistent airway obstruction without any COPD symptom [OBS group]) and clinically-defined COPD (i.e., persistent airway obstruction with at least one COPD symptom [COPD group]), all detected by screening. A spirometry was performed in 5095 subjects aged 40-75 years. Persistent airway obstruction was defined as a post-bronchodilator FEV1FVC In total, 138/5095 subjects (2.70%) had persistent airway obstruction. Among them, 78 had at least one COPD-related symptom (COPD group), 52 have none of the COPD-related symptoms (OBS group) and 8 had missing data and were not analyzed. The main characteristics are in Table 1. Mean FVC was normal (z-score>-1.64) in both groups. By contrast, mean FEV1 was abnormal only in the COPD group (mean z-score A significant subset of subjects detected by screening with persistent airway obstruction are asymptomatic; a majority of these asymptomatic subjects have normal FEV1.