BACKGROUND: Many studies have suggested the association between asthma and obesity both of which are important chronic health problems and socioeconomic problems. There are few studies about the association of adults in foreign nations and the association of all ages in Korea, especially based on the representative population. OBJECTIVE: Authors analyze the association between asthma and indices such as BMI (body mass index), age, gender, smoking, alcohol drinking and diet habit in Korea National Health and Nutrition Survey. METHOD: National Survey was done from November to December 2001 and this study enrolled 27,331 men and women above 19 years of age. A structured questionnaire, weight and height were used to collect information. Obesity is defined above 25 kg/m2 of BMI. The criterion of asthma is a diagnostic history by medical doctor. RESULT: The overall prevalence of asthma in this study is 1.54% (male 1.50%, female 1.57%). The prevalence is higher in elderly (> or =60), smokers, obese person, someone who has low educational level and does not have current partner. The significant predictors of asthma in multiple logistic regression are BMI (female OR=1.685 (95% CI=1.047~2.713)), age (male OR=3.250 (95% CI=0.999~10.567), female OR=6.798 (95% CI=1.583~29.195)), educational level (male OR=5.381 (95% CI=1.857~15.598)) and alcohol drinking (OR=0.549 (95% CI=0.323~0.933)). CONCLUSION: Obesity is a risk factor of asthma in women. Old age and low educational level are social risk factors in asthma in men.