In May, Xiao Ding from Yiwu City, Zhejiang Province, was admitted to the respiratory ward of Beijing Chaoyang Hospital. Xiao Ding, 23 years old, developed shortness of breath after activity with no obvious cause six months ago, and felt breathless when he went up three floors. In January of this year, Xiao Ding had a sudden onset of dyspnea and chest pain, and was diagnosed with “right spontaneous pneumothorax” at a local hospital, where he underwent “right alveolar resection” and “pleural fixation” in thoracic surgery. Three months ago, he developed thirst, polyuria and nocturia, which was diagnosed as “complete central uremia” in the local hospital. However, Ding still felt shortness of breath, and a chest CT showed multiple cystic and nodular shadows in both lungs. What was wrong with Ding, who was in good health? After detailed questioning by the respiratory doctor, it was discovered that Ding had been smoking since he was 17 years old and had been smoking for 5 years, smoking 20 cigarettes a day. After further tests, Ding was diagnosed with pulmonary langerhans histiocytosis (PLCH for short). Adult PLCH, also known as histiocytosis X, is a rare disease that occurs in the majority of smokers, and the onset of PLCH is closely related to smoking. The clinical presentation of PLCH varies, with some patients having mild respiratory symptoms that can be easily missed or diagnosed when the disease becomes more severe with dry cough and dyspnea after activity. and recurrent. Chest imaging is characteristic, showing multiple thick-walled cystic cavities and nodules in both lungs, predominantly in the upper and middle lung fields, but care should be taken to differentiate them from other lung diseases, such as emphysema, pulmonary lymphangioleiomyomatosis, and congenital lung cysts. Lung histopathology is the “gold standard” for the diagnosis of PLCH. The main histopathologic feature is the presence of scattered stellate interstitial nodules in the lung tissue centered on the fine bronchi. Immunohistochemistry showed positive CD1a and S-100 in Langerhans cells. 5 patients with PLCH have been diagnosed and treated promptly at our hospital in the past 1 year. The doctor instructed Ding to quit smoking and his condition gradually improved after quitting. Young people who smoke heavily should pay attention to identify PLCH when they have recurrent pneumothorax or multiple cystic shadows in the lungs.