Smoking traditionally has not been considered as a cause of bronchiectasis. However, few studies have evaluated the association between smoking and bronchiectasis. This study aimed to investigate the association between smoking status and bronchiectasis development in young adults. This study included 6,861,282 adults aged 20–39 years from the Korean National Health Insurance Service database 2009–2012 who were followed-up until the date of development of bronchiectasis, death, or 31 December 20 ...