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Regression of total width on length of the second metacarpal of the hand was used to establish three categories of bone proportions in a large sample of normal children aged three through nine years of age. Comparisons between these categories in stature, number of ossified centers of the hand and wrist and six radiographic variables were performed on the normal sample of children and the analysis extended to a sample of subjects who were cognitively retarded. Results from the normal sample show that for a given bone length, disproportionately narrow metacarpals have decreased cortical areas and bone volumes, whereas disproportionately wide metacarpals have increased bone values. Among boys, ossification is delayed by one or more centers for narrow-shaped bones. Among both sexes, ossification is advanced one or more centers for wide-shaped metacarpals. Multiple regression as well as age-specific analyses of these data indicate that these categories are more closely associated with medullary diameter than cortical thickness, and are independent of stature, chronological age and metacarpal length. Compared with the normal group, the sample of growth-impaired children showed an overall reduction in cortical bone formation and a fourfold increase in the incidence of narrow metacarpals.