Abstract: Skeletal ages were assessed for 4902 pairs of hand--wrist and knee radiographs of children aged 2 to 17 years. The FELS method was used to assess the hand-wrist and the RWT method was used to assess the knee. The mean absolute differences, within ageand sex-specific groups, ranged from 0.34 to 0.87 years. The SD of the differences ranged from 0.31 to 0.68 years and, like the means, tended to increase with age until about 8-l1 years. The means and SD were generally larger for the boys than for the girls except after 14 years. Within age-and sex-specific groups, the maximum differences were from 1.45 to 2.99 years. These maximum differences changed irregularly with age but tended to increase until 11 years in the boys and 9 years in the girls. These large absolute differences between the skeletal ages of the hand -wrist and the knee cannot be explained completely by the effects of observer errors. These skeletal ages are not interchangeable; in at least 5% of children, the choice of the area for skeletal age assessment will markly influence the evaluation of individuals, the prediction of adult stature and the selection of ages for epiphyseadeses.

Key words: Skeletal maturity; Hand-wrist; Knee; Skeletal age