Stress fractures are extremely common lesions that occur in specific areas and are related to specific activities. They are caused by increased muscular activity on bones that are not yet ready to take the increased pull of the involved muscles. The insufficiency type of stress fractures found in patients with bone of diminished mineral content is being recognized more often as increasing numbers of middle-aged and elderly persons are becoming more physically active. A variety of imaging studies can be used to diagnose stress fractures. Radionuclide bone scanning and MR imaging often show abnormalities early in the course of the injury. However, when radiographs appear normal, findings on scintigrams may be more suggestive of the proper diagnosis. In patients with suspected stress injury, radiographs should be obtained a second time, 1-2 weeks after the initial study. Biopsy should be avoided until evidence is clear-cut that the lesion has not changed over a short time.