The objective of this study was to gain normal reference values and to evaluate gender differences in total and regional body composition changes according to age and Tanner stage by dual-energy X-ray absorptiometry in Korean. Four hundred and forty-nine healthy subjects, aged 5-20 yr were enrolled. Until 9 yr of age, males had a higher lean tissue mass and a lower percent body fat (%BF) than the females (12.6% vs 10.0%, p<0.01). These differences were not evident from 10 to 12.9 yr because of early pubertal progression in girls. After 13 yr, a significant sex difference in the body compositions were observed again. In late teens, females have higher %BF than males (25.6% vs 12.3%, p<0.01). However, females have lower android-gynoid percent fat ratio than males at Tanner stages (TSs) 4 and 5 (p<0.01). These differences are because of significant increase of gynoid lean tissue mass after 13 yr in males. The reference data would be useful for future research related to growth and obesity in Korean children and adolescents.