In a cadaveric study in seven hands, the mathematical relationship between extensor tendon excursion and joint motion (wrist, m.p., p.i.p. and d.i.p.) has been investigated. This has been found to be linear at all joints, allowing the mean tendon excursions corresponding to ten degrees of joint motion to be calculated for each of the above joints for all five rays of the hand. A table of these excursion values is presented as a reference for calculation of clinical problems.