Jeong Uk Lim,1 Jae Ha Lee,2 Ju Sang Kim,3 Yong Il Hwang,4 Tae-Hyung Kim,5 Seong Yong Lim,6 Kwang Ha Yoo,7 Ki-Suck Jung,4 Young Kyoon Kim,8 Chin Kook Rhee8 1Division of Pulmonary, Critical Care and Sleep Medicine, Department of Internal Medicine, St Paul’s Hospital, College of Medicine, The Catholic University of Korea, 2Division of Pulmonology, Department of Internal Medicine, Inje University College of Medicine, Haeundae Paik Hospital, Busan, 3Division of Pulmonary Medicine, Department of Internal Medicine, Incheon St Mary’s Hospital, College of Medicine, The Catholic University of Korea, Incheon, 4Division of Pulmonary, Allergy and Critical Care Medicine, Department of Internal Medicine, Hallym University Sacred Heart Hospital, Hallym University College of Medicine, Anyang, 5Division of Pulmonary and Critical Care Medicine, Hanyang University Guri Hospital, Hanyang University College of Medicine, Guri, 6Division of Pulmonary and Critical Care Medicine, Department of Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, 7Division of Pulmonary, Allergy and Critical Care Medicine, Department of Internal Medicine, Konkuk University School of Medicine, 8Division of Pulmonary, Allergy and Critical Care Medicine, Department of Internal Medicine, Seoul St Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea Introduction: A low body mass index (BMI) is associated with increased mortality and low health-related quality of life in patients with COPD. The Asia-Pacific classification of BMI has a lower cutoff for overweight and obese categories compared to the World Health Organization (WHO) classification. The present study assessed patients with COPD among different BMI categories according to two BMI classification systems: WHO and Asia-Pacific. Patients and methods: Patients with COPD aged 40 years or older from the Korean COPD Subtype Study cohort were selected for evaluation. We enrolled 1,462 patients. Medical history including age, sex, St George’s Respiratory Questionnaire (SGRQ-C), the modified Medical Research Council (mMRC) dyspnea scale, and post-bronchodilator forced expiratory volume in 1 second (FEV1) were evaluated. Patients were categorized into different BMI groups according to the two BMI classification systems. Result: FEV1 and the diffusing capacity of the lung for carbon monoxide (DLCO) percentage revealed an inverse “U”-shaped pattern as the BMI groups changed from underweight to obese when WHO cutoffs were applied. When Asia-Pacific cutoffs were applied, FEV1 and DLCO (%) exhibited a linearly ascending relationship as the BMI increased, and the percentage of patients in the overweight and obese groups linearly decreased with increasing severity of the Global Initiative for Chronic Obstructive Lung Disease criteria. From the underweight to the overweight groups, SGRQ-C and mMRC had a decreasing relationship in both the WHO and Asia-Pacific classifications. The prevalence of comorbidities in the different BMI groups showed similar trends in both BMI classifications systems. Conclusion: The present study demonstrated that patients with COPD who have a high BMI have better pulmonary function and health-related quality of life and reduced dyspnea symptoms. Furthermore, the Asia-Pacific BMI classification more appropriately reflects the correlation of obesity and disease manifestation in Asian COPD patients than the WHO classification. Keywords: body mass index, COPD, comorbidity