A naturally-occurring fracture of the distal radius and ulna in a skeletally immature fin-whale, Balaenoptera physalus, appeared to be failing to heal. When compared to the response to fracture in the skeletally immature human and to other terrestrial mammals, this animal did not show any endosteal and only minimal subperiosteal callus, even though the fractures appeared to be several weeks, if not months old. This suggests that the larger ceteceans may not be able to respond appropriately to skeletal injury in the major structural units of the flipper.