Isolated displaced fractures of the posterior facet of the talus do occur, and they can be diagnosed if one is alert to this possibility when studying the roentgenograms of the ankle. It is possible that it is this injury undiagnosed that causes some of the chronically painful so-called sprained ankles that are such problems at times. Certainly, in every case of ankle sprain resistant to the usual conservative treatment, the roentgenograms should be reviewed and repeated with this fracture in mind. Early diagnosis appears to be of paramount importance. Early open reduction and fixation may avoid prolonged disability and pain.