We believe that our study have some merits and could contribute more to clinical practice. First, previous studies of causes of chronic cough were performed in a relatively small number of patients seen in a specific clinic, so risked selection bias. In this study, although the number of patients with chronic cough may seem small, the survey population selected is regarded as representative of the Korean general population. Second, most of the previous studies excluded smokers or patients with abnormal chest radiographs, and clinicians have had questions about the general frequency of chest radiographic abnormalities and the different characteristics of smokers. Our data showed not only a high prevalence of cigarette smoking (47.7%) in subjects with chronic cough, but also a strong impact of smoking (OR 3.16) on the prevalence of chronic cough independent of underlying diseases. Third, our study found that the prevalence of abnormal chest radiographs, which could be a cause of chronic cough, is 4.0% in the general population. However, the OR for chronic cough was higher than for COPD or UACS, underscoring the importance of chest radiography, especially in a region with a high prevalence of tuberculosis.