Seventy-one cases of ankle fractures in children were studied. An analysis of the fracture lines involving the distal tibial and fibular epiphyses were done. A new classification is proposed based on the position of the foot at the moment of trauma and the direction of the abnormal force. Four mechanisms were considered, grades were described for each mechanism and each grade always occurred in the same order. In almost half of the cases, the supination-inversion mechanism was responsible for the injury. A correlation with the physeal injury classification of Salter and Harris is imperative, since complications such as varus deformity of the ankle are common when a Salter-Harris III or IV injury is present. The proposed classification has an important practical use. It facilitates closed reduction, because once the mechanism of injury is known, reduction is obtained by reversing the direction of abnormal force and immobilizing the foot in the opposite position given by the mechanism.