The purpose of this study was to investigate the prevalence of allergic diseases and its related factorsin Korean adolescents. The subjects were 72,435 middle and high school students. The data were analyzed by ${\chi}^2$ test and multiple logistic regression analysis. The prevalence of asthma, allergic rhinitis, and atopic dermatitis was 9.3%, 30.6%, and 23.4%, respectively. According to multiple logistic regression analysis, asthma was associated with gender, age, economic state, obesity, stress, sleep satisfaction, secondhand smoking, drug use, other allergic diseases and physical activity. Allergic rhinitis was associated with age, economic state, residential area, type of residence, obesity, stress, sleep satisfaction, smoking experience, secondhand smoking, alcohol drinking, other allergic diseases and physical activity. Finally, atopic dermatitis was associated with gender, age, economic state, residential area, obesity, stress, other allergic diseases and physical activity. Conclusion: These results will provide database for prevention and management of allergic diseases.