Obesity poses a significant risk factor of chronic disease for individual’s health. In order to understand the prevalence of obesity in adolescents, and compare the results using various methods for estimating body composition, a cross-sectional survey was conducted in 1991. A systematic sampling procedure by cluster was employed. 1168 subjects were selected from Taipei City Junior High Schools which included 47,173 seventh graders. The subjects were asked to complete a set of questionnaires. A measurement of height, weight, and skinfolds was also administered. When a skinfold exceeding the 85th percentile, a BMI exceeding the 85th percentile, and a weight more than 20% of average weight were adopted as criteria, the prevalence rates of obesity were 15.0-17.3% for males and 14.8-15.6% for females. The correlation coefficients of 0.66 to 0.98 between indices were found. The concordance rates for screening obesity by different indices were 89.3% to 93.5%. It is expected to establish adolescent body composition norms periodically. A distribution of body composition index can be developed using the height and weight data of students in each school. Based on the distribution, the obeses will be selected. It suggests to provide a weight control program in school as soon as possible.