The purpose of this study was to determine differences in body size, composition and structure between three somatotypes of Japanese college-aged women. The study sample consisted of 30 sedentary female college students between 18 and 20 years of age. Ten subjects had an endomorphic ectomorph somatotype (mean weight 41.95 kg), 10 had an endomorph-ectomorph somatotype (mean weight 47.12 kg) and the remaining subjects had a mesomorphic endomorph somatotype (mean weight 55.37 kg). The mean heights for these groups did not differ significantly. The mesomorphic endomorph group had a higher gross weight and a higher percentage of all adipose variables than the other two groups, though these measurements were not significantly different between the endomorph-ectomorph and the endomorphic ectomorph groups. The mean lean body weight (LBW) for the mesomorphic endomorph group was significantly larger than that of the other two groups. The endomorph-ectomorph group had the next largest LBW, and the mean for the endomorphic ectomorph group was significantly smaller than that of the other two groups. Inversely, mean values of LBW/weight(WT), LBW/total adipose tissue weight (TATW) ratio and total body water/WT were significantly lower for the mesomorphic endomorph group than for the other two groups. Furthermore, the ratios of internal adipose tissue to weight (IATW)/WT and subcutaneous adipose tissue to IATW (SATW)/IATW did not differ significantly between groups. In conclusion, college-aged women of different somatotypes within the same age and height range varied in body composition. Consequently, the notion of a small frame is incorrect. An accurate assessment of the human body's composition may provide a valuable insight into the ideal weight for optimal physiologic function.