In the diagnostic analysis of acute injury to the lateral ankle ligaments, ankle arthrography and plain film stress examination play an important role. Inasmuch as the treatment of choice, whether conservative or surgery, and insofar as the therapeutic results may be determined by the extent of injury, it is important to have access to quantitative information on the functional properties of the involved ligaments at the time of the initial diagnostic studies. This can be obtained by measuring the strain on the anterior talofibular (tf) and calcaneofibular (cf) ligaments as a function of pressure applied to the distal tibia. Any device that ensures that the externally applied pressure is proportionally carried through to the ligaments can be used for this purpose. The results of 25 quantitative stress examinations using a Telos stress device are compared with arthrography findings and findings at surgery. Stress examination correlates well with both arthrographic and operative findings. The method is also useful for the evaluation of chronic ankle instability, follow-up examinations, and for the detection of vestiges of previous trauma of the contralateral ankle. The procedure is straightforward and noninvasive and can be performed within 15 minutes.