The mathematical relationship between the lengths of the metacarpals and phalanges is important in hand surgery because of its role in determining the lengthening of the tubular bone size or the length of a prosthesis. The purpose of the present study is to perform the measurements on the hand radiographs, and to determine possible mathematical relations between the lengths of the metacarpals and phalanges. The lengths and widths of metacarpals and phalanges were measured in millimeters on hand roentgenograms of 100 normal voluntary subjects (50 men, 50 women) and the results were evaluated with a descriptive analysis test. The relations between the lengths of the metacarpals and phalanges were mathematically investigated on several sets of data. Unchangeable proportions between the metacarpals and phalanges lengths were found and formulated. Because any defects or faults of the hand, especially shortness, can corrected with current improved surgical techniques, a knowledge of the morphometric relations between the lengths of metacarpals and phalanges may be useful for such surgical interventions.