Abstract: Sibling correlations are reported for FELS skeletal age from 2622 mixed longitudinal hand-wrist radiographs of 285 boys anl 276 girls. Because the observed correlat1ons were ir-regular across age, they were s1oothed using kernel regression. The brother-sister correlations'were generally lower than those for the cther types of sibling pairs, but they were s1milar to thebrother -brother correlations after 11 years. The sister-sister correlations were considerably higher than the brother-brother and brother-sister correlations after 12 years. The present data donot provide clear evidence of involvement of the X chromosome in the timing of skeletal matu-ration, but after 12 years the present data suggest such an involvement.

Key words: Skeletal age; Siblings; Genetic control