The FELS method of assessing the skeletal maturity of the hand-wrist differs from the Greulich-Pyle and Tanner-Whitehouse methods in the observations made, the provision of a range of shapes to which maturity indicator grades can be assigned and in the statistical methods used to construct the scale of skeletal maturity. The FELS method for the hand-wrist was developed using 13,823 serial radiographs of the left hand-wrist of boys and girls in the Fels Longitudinal Study. One hundred-thirty possible indicators were originally identified. Eighty-five graded and 13 metric indicators were selected on the basis of an indicator's ability to discriminate between children at the same chronological age, its universal appearance, reliability, validity, and completeness. The subset of FEELS maturity indicators assessed at a chronological age are analyzed with a microcomputer program that provides the skeletal age and the standard error of the estimate for that skeletal age. Comparison among hand-wrist skeletal age assessments for children in the Fels Longitudinal Study by the FELS, Greulich-Pyle, and Tanner-Whitehouse methods indicate that the FELS method is the more appropriate method for the present population of United States children.