Clinical experience with 99mTc-polyphosphate scintigraphy in more than 200 patients with suspected stress fractures is presented. Stress fractures occur in bone which is weakened as a result of accelerated physiological change induced by excessive muscular and mechanical activity. Unlike traumatic fractures, they are not accompanied by radiographic abnormality early in their course. Bone scintigraphy is sensitive enough to detect the physiological alterations found in stress fractures and was responsible for decreased morbidity in this series of patients due to early diagnosis.