The monthly body weight data of school children in different regions, the school A in urban area of Tokyo, the school B and C in rural areas of Gunma and Tochigi prefectures, were investigated in order to compare the regional patterns of seasonal variation in weight growth. The seasonal factors of each region and those of each children were calculated by a time-series analysis. The results obtained were as follows. 1) In all regional groups, the highly significant seasonality (p<0.0001) were observed. The seasonal patterns of low in summer, especially in July, were the same in all regional groups. However, the months in which the high values appeared were different among the groups. The amplitudes of seasonal variation were smaller in the children of school A than in the children of school B or C. 2) From the analysis of the seasonal patterns of each child, the minimum values in seasonal factor appeared in July in many children, and it was remarkable in the children of school B and C. 3) The effects of months on variation in weight growth were different between sexes, from the fact that the F-values in the stable seasonality test were much higher in boys than in girls.
