Bronchiolitis refers to a condition that is associated with the nonspecific inflammatory injury to the small airways, often sparing a considerable portion of the interstitium. Until now, the prevalence, mortality, comorbidities, and medical expenditure for bronchiolitis have not yet been elucidated. We used 2% sample data of NHIS (National Health Insurance Service), which is stratified random sampling of 50 million Koreans considering age, sex, residence area, income, etc. We defined bronchiolitis except acute bronchiolitis (J21) as a patient with a diagnostic code of J448 or J684 in patients who had a CT scan of patients over 20 years old who visited clinic or hospital in South Korea from 2002 to 2013. We excluded acute bronchiolitis (J21) and cystic fibrosis (E84). The overall prevalence of bronchiolitis was 688 cases per 1,000,000. In terms of comorbidity, asthma (52.2%) was the most common, followed by HTN (43.7%), GERD (30.6%), DM (22.8%) and osteoporosis (17.9%). Other comorbidities were cerebrovascular disease (16.9%), angina (14.4%) and peripheral vascular disease (13.4%). Medicare spending on bronchiolitis averaged about 465,000 won (350 euros) per person per year. The mortality rate was the highest due to any cancer (512 cases, 6.2%), followed by bronchiolitis (270 cases, 3.3%), followed by cerebrovascular disease (90 cases, 1.1%), and pneumonia (68 cases, 0.8%). Among the cancer mortality, 229 cases (2.8%) of lung or bronchi cancers accounted for half of all cancers. In conclusion, bronchiolitis is an underestimated, burdensome disorder with various medical comorbidity, and further study is needed for further conceptualization and pathobiology.