We compared the clinical characteristics of the subjects according to current smoking status, UACS, COPD, asthma, and abnormal chest radiographs to determine whether associated symptoms could be used to differentiate causes of chronic cough. The most frequently associated symptom was phlegm (75.9% ± 3.0%). All groups showed a high frequency of chronic sputum production, but the frequency was significantly higher in current smokers (86.9% ± 3.7%). The UACS group reported more episodes of dyspnea and night sweats, and the COPD group reported more occurrences of blood-tinged sputum. However, there was no specific clinical characteristic suggesting asthma or chest radiographic abnormality (Table 5). When clinical characteristics were compared between subjects with a single cause and those with 2 or more causes, subjects with multiple causes complained more frequently of dyspnea and weight loss (Table S2).