Abstract: The skeleton is one of the most common metastatic sites in patients with maligancy skeletal metastases are clinically significant because of associated symptoms, complications such as pathological fracture and their profound significance for staging, treatment and prognosis. Detection of bone metastases is, thus, an important part of treatment planning. The frequency with which metastases are detected varies considerably with the type of primary tumor and with the methodology utilized for detection. Bone scan is the most common modality in detection bone metastases. But its accuracy in early stage of bone metastases is limited. ¹⁸F-NaF and ¹⁸F-FDG are two different positron tracers, which can detect bone metastases by osteoblastic reaction of bone to the presence of tumors and directly tumor imaging, separately. Combination with the high resolution of PET, especialy the PE-CT which also provide a better anatomic localization, the accuracy of detection of bone metastases was improved significantly.