We describe a technique for measuring the Stiffness of regenerate bone after leg lengthening. This allows early identification of slow healing by reference to normal patterns. We determined the time of removal of the fixator from clinical and radiological information independent of the stiffness result. In a series of 30 leg lengthenings there were no refractures when the tibial stiffness had reached 15 Nm/° or the femoral stiffness 20 Nm/°. Three refractures occurred at lower stiffness values. The technique is simple to perform, will allow a reduction in plain radiography and is recommended for routine postoperative management