The exact mechanism of ankle and foot fracture in motor vehicle crashes have been little studied because detailed medical records of injured occupants have bene lacking. A study of 23 frontal impacts for which detailed information, including x-rays, is available was conducted to identify common mechanisms of fracture and examine the role of footwell intrusion in ankle and foot injury. The medical files made possible the association of fracture mechanisms with injury locations within and near the ankle and the positive identification of four common fracture mechanisms: inversion or eversion, direct vertical force, dorsiflexion, and direct side force. Inversion or eversion was identified as a fracture mechanism in 15 of 23 injured ankles or feet (65 percent) and in 12 or 13 malleolar injuries (92 percent). This stands in contrast to other recent work in which dorsiflexion was postulated to be a prominent injury mechanism. Concurrent vehicle investigation made it clear that footwell intrusion plays a large role in injuries induced by inversion or eversion. The importance of intrusion as a contributing cause of ankle and foot injuries is currently unrecognized in U.S. vehicle safety standards.