The purpose of the present study was to evaluate the normal process of cortical bone acquisition during childhood and adolescence, and the relationship between speed of sound (SOS), measured by the Sound Scan 2000 system, and linear growth. A total of 1689 healthy Japanese children and adolescents (862 males and 827 females, aged 7-19 years) were enrolled in the study. SOS (m/s) was measured at the right tibial midshaft and the standard SOS values in the children and adolescents were generated. Various growth parameters were also measured. SOS of tibia increased significantly with age in both males and females (P < 0.001 each). In both sexes, a spurt in SOS was noted 1 year after the standard age at which Japanese peak height velocity (PHV; cm/year) occurs, and SOS increased markedly after the age at which the length of tibia reached a maximum. Multiple regression equations for SOS were generated as a function of various growth parameters; for males, SOS = 3047 + 6.2 x height (cm) + 2.1 x weight (kg) - 9.8 x length of tibia (cm) (R2 = 0.50; P < 0.001) and for females, SOS = 2713 + 10.3 x height (cm) + 1.8 x weight (kg) - 15.5 x length of tibia (cm) (R2 = 0.49; P < 0.001). In both sexes, SOS correlated positively with body height and weight, but negatively with length of tibia. Our results indicate that SOS is quite useful for evaluating cortical bone status in children and adolescents; the results of these measurements may provide an explanation for the relative weakness of the mechanical properties of the bone during childhood and adolescence.