The purpose of this study was to examine the stability of somatotypes of 63 boys in Saskatoon, Canada who were followed from 7 to 16 years of age. Somatotype photos were taken annually and rated by a criterion rater (BH-R). Comparisons were made longitudinally across all years using repeated-measures ANOVAs of the whole somatotype (S), somatotype attitudinal means (SAM), analysis of categories, separate components (endomorphy, mesomorphy, ectomorphy), and partial correlations. In the first year, the means were age = 7.1 yr, height = 121.0 cm, mass = 22.8 kg, S = 2.9-3.6-1.6, and SAM = 1.1. In the last year, the means were age = 16.7 yr, height = 172.6 cm, mass = 59.9 kg, S = 2.5-4.0-3.7, and SAM = 1.4. Mean somatotypes across years were different [F = 67.9, P < .01], with the largest differences between 7-10 yr and 14-16 yr. These differences were largely due to significant increases in mesomorphy (F = 24.6, P < .01) and ectomorphy (F = 159.9, P < .01). Partial correlations between ages for each component, with the other two held constant, revealed poor predictions for three or more years apart (r < .35). Thus, both group and individual somatotypes changed between 7 and 16 years of age. The overall pattern was from endo-mesomorph through central to mesomorph-ectomorph somatotypes. The trends are similar to those observed in comparable samples from other countries. Am. J. Hum. Biol. 9:257-272, 1997. Β© 1997 Wiley-Liss, Inc.