Injuries to the ankle are common in children. We investigated whether decreased dorsiflexion predisposes to such fractures and sprains. Passive dorsiflexion in children with ankle injuries was compared with that in a control group of patients with a normal ankle. The uninjured side was examined to determine flexibility in those patients with ankle injuries. In 82, the mean dorsiflexion was 5.7 degrees with the knee extended and 11.2 degrees with the knee flexed. In 85 controls, the mean dorsiflexion was 12.8 degrees with the knee extended and 21.5 degrees with the knee flexed (p < 0.001, Student's t-test). There was a strong association between decreased ankle dorsiflexion and injury in children. A flexible triceps surae appeared to absorb energy and protect the bone and ligaments, while stiffness predisposed to injury. We suggest that children with tight calf muscles should undergo a regimen of stretching exercises to improve their flexibility.