Evaluation of anterior laxity of the ankle joint complex is a difficult clinical problem. Currently, the prime determinant for anterolateral ligament function is the subjective manual examination of anterior laxity of the ankle joint complex. An instrumented dynamic test was developed for objective measurement of anterior laxity of the ankle joint complex. The principle of the test was to apply a force-impulse to the calcaneus, within the muscle reflex time, and to measure anterior-posterior and mediolateral rotation. The test was performed on a cadaver specimen and on 15 volunteers of which five subjects suffered from chronic one-sided lateral ankle ligament instability. In the cadaver test, anterior translation values increased from 5 to 11 mm, after cutting the anterior talofibular ligament and subsequently cutting the calcaneofibular ligament. In the 10 normal subjects, the mean anterior translation value was 6.7 mm (+/-1.9 mm). The relative variation of the test result within a measurement session was 2.5% (+/-1.6%). Between the sessions the relative laxity variation was 2.6% (+/-2.6%). In the ten normal subjects the mean right-left difference was not significantly different from zero. In four out of the five patients it was more than 2mm. As in the cadaver test in all measurements, the mediolateral rotations were small (<2.5 degrees ). The volunteers complained about same pain at the heel after multiple test sessions. In conclusion the dynamic, functional test appears to be capable of objectively measuring a value for anterior laxity of the ankle joint complex reflecting the functional status of the anterolateral ankle ligaments.