The aims of the present study were to contrast the distance and velocity curves for height, body mass and somatotype between active (n = 33) and sedentary (n = 15) boys studied annually between 12 and 15 years. Raw measurements were rescaled and aligned according to peak velocity in height (PHV). The sedentary boys were taller up to and including PHV, active boys being taller after PHV (P > 0.05). The sedentary group had a PHV of 8.5 +/- 1.2 cm year-1 and the active group one of 9.5 +/- 1.5 cm year-1 (P < 0.05). Their ages at PHV were 14.1 +/- 0.8 and 14.2 +/- 0.9 years, respectively (P > 0.05). The active boys were lighter before PHV but heavier afterwards. Peak body mass velocities (PBMV) were larger for the active children (9.1 +/- 2.7 kg year-1) compared to the sedentary children (8.0 +/- 2.6 kg year-1) (P > 0.05). At PBMV, the active boys were aged 14.3 +/- 0.8 years and the sedentary boys 14.5 +/- 0.7 years (P > 0.05). The representative somatotype for the sedentary group was a mesomorphic ectomorph. For the active group, ectomorphic mesomorphs and mesomorphic ectomorphs were the most prominent. The sedentary children (overall mean 2.4-3.4-4.7) showed an increase in endomorphy and a decrease in mesomorphy and ectomorphy. In contrast, the active children (overall mean 2.3-3.9-4.0) demonstrated reduced endomorphy with mesomorphy and ectomorphy remaining fairly uniform. Velocities showed mesomorphy to be the most stable component in both groups (-3.0 to +0.1 units year-1). Endomorphy and ectomorphy fluctuated to a greater extent but never quite reached a velocity of one-half unit a year. Whole somatotype analyses identified significant differences between groups at PHV (P < 0.05), individual component analyses at PHV and +1 year PHV (P < 0.05).