The distance between the midpoint of the distal radial epiphyseal growth plate and the proximal end of the third metacarpal offers a useful measure for determining wrist size. Standards of this distance as compared to intermetacarpal width and second metacarpal length are presented. These measures (or ratios) should be useful in evaluating patients with juvenile rheumatoid arthritis and a number of congenital malformation syndromes, particularly when the carpals are still not fully ossified. Shortening of the carpus occurs in multiple epiphyseal dysplasia, the otopalatodigital syndromes, Turner syndrome, arthrogryposis, and in juvenile rheumatoid arthritis. A relatively large carpus is present in achondroplasia.