Om P Kurmi,1 Liming Li,2,3 Jenny Wang,1 Iona Y Millwood,1 Junshi Chen,4 Rory Collins,1 Yu Guo,2 Zheng Bian,2 Jiangtao Li,5 Biyun Chen,6 Kaixu Xie,7 Weifan Jia,8 Yali Gao,9 Richard Peto,1 Zhengming Chen1 On behalf of the China Kadoorie Biobank Collaborative Group 1Nuffield Department of Population Health, Clinical Trial Service Unit and Epidemiological Studies Unit (CTSU), University of Oxford, Oxford, UK; 2Department of Epidemiology and Biostatistics, School of Public Health, Peking University, 3Chinese Academy of Medical Sciences, Dong Cheng District, 4China National Center for Food Safety Risk Assessment, Beijing, 5NCDs Prevention and Control Department, Huixian CDC, Huixian, Henan, 6NCDs Prevention and Control Department, Hunan CDC, Changsha, 7NCDs Prevention and Control Department, Tongxiang CDC, Zhejiang, 8NCDs Prevention and Control Department, Liuyang CDC, Baiyikengdao, Liuyang, Changsha, Hunan, 9NCDs Prevention and Control Department, Sichuan CDC, Sichuan, Mainland China Purpose: In adult Chinese men, smoking prevalence is high, but little is known about its association with chronic respiratory disease, which is still poorly diagnosed and managed. Methods: A nationwide study recruited 0.5 million men and women aged 30–79 years during 2004–2008 from ten geographically diverse areas across the Mainland China. Information was collected from each participant regarding smoking and self-reported physician diagnosis of chronic bronchitis/emphysema (CB/E), along with measurement of lung function indices. Logistic regression was used to yield sex-specific odds ratios (ORs) relating smoking to airflow obstruction (AFO), defined as forced expiratory volume in 1 second (FEV1)/forced vital capacity (FVC)