Trauma has been indicted as the cause of some types of bone cysts, but the development of a cyst in the course of healing of a fracture in a long bone has not been previously reported. A case is presented in which a bone cyst developed at a fracture site in the fibula. The evolution of the lesion is documented by serial roentgenograms and its pathological features are presented. The pathogenesis of this cyst and its possible relationship to other cystic lesions is discussed.