In briefACL injuries in children result in adultlike chronic instability problems. Physical tests and radiographs guide the diagnosis. Treatment depends on whether the ACL injury is an intrasubstance tear or, what is more common, an avulsion fracture of the tibial eminence. A case report of an 11-year-old boy describes a typical avulsion injury. Treatment of avulsion injuries consists of cast immobilization and open reduction and fixation for a displaced fragment.