99m-Tc--polyphosphate bone imaging was useful in distinguishing Legg-Perthes disease from other childhood hip disorders in 40 patients. In 33 Legg-Perthes patients, imaging provided earlier and more accurate information concerning the extent of the necrotic and revascularization process involving the hip than radiographs alone. This advantage could both facilitate treatment selection and provide a more objective baseline from which to judge treatment results. Preliminary experience also suggests that the technique may offer some insight into the pathogenesis of Legg-Perthes disease.