We report a case of metastatic pathologic fracture of femoral shaft, whose primary cancer was ascertained by positron emission tomography-computed tomography (PET-CT). The abnormally increased biological activity of the space-occupying lesion of the lung was clearly demonstrated by PET-CT. Moreover, the occult bony metastatic lesions were confirmed with evidence of altered biologic activity. The PET-CT should be regarded as a valuable work-up tool for the orthopaedic management of metastatic pathologic fracture of a skeleton, all-the-more as a functional metabolic imaging tool.