One hundred and thirty fractures of the femoral neck treated with sliding screw-plate or sliding nail-plate were followed for up to 65 months postoperatively. Throughout the observation period the yearly incidence of necrosis of the femoral head was between 5 and 10 per cent, as estimated by the life table method, and after 5 years 37 per cent of the patients with united fractures had developed necrosis of the femoral head. The cases of necrosis were all characterized radiographically by one or more areas of subchondral cortical depression, generalized subchondral fragmentation or isolated patches of sclerosis. It is concluded that estimation of the frequency of femoral head necrosis after fracture of the femoral neck requires long-term follow-up and reliable, reproducible radiographical criteria for necrosis of the head. Because of the high mortality of patients sustaining these fractures, statistical methods employing censored data should be used.