Inversion sprains of the lateral ligaments of the ankle are one of the most common of all sporting injuries. While the strains in the anterior talofibular (ATFL) and calcaneofibular (CFL) ligaments have been measured in quasi-static conditions, the dynamic strains during an actual traumatic event have not been determined. The present investigation determined the strains and strain rates in the ATFL and CFL during an in vitro inversion sprain. The ATFL tended to have higher strain and strain rate values than the CFL, which may explain why it is more often injured than the CFL.