Design: Cross-sectional validation study Subjects: 221 COPD patients who ranged in age from 25 to 93 years old, treated at the Ho Chi Minh city University Medical Center from 2005 to 2007.Results: The study has shown that COPD patients in stage IV who are male and younger than 60 years old have lower BMI than those in other stages, and group with BMI <18.5 has the lowest% postFEV1.