This 68 y/o vietnamese female presented with a history of left lower leg pain for one month. Selected CT, MRI, and plain film images are shown above. There is a subtle area of sclerosis on the plain film images. The CT shows early periosteal new bone formation with an intact cortex and minimal trabecular disruption. MRI images demonstrate high signal surrounding the tibial shaft presumably representing edema. There is a band like area of signal change in the proximal tibial marrow. We considered stress fracture a likely etiology but felt unable to exclude atypical osteomyelitis or tumor with certainty. A bone biopsy was performed and pathologic evaluation including an opinion from the AFIP (Armed Forces Institute of Pathology) yielded a diagnosis of stress fracture.