Positron emission tomography(PET) is an imaging technique that produces images reflective of tissue biochemistry rather anatomy. The great versatility of PET and its potential of direct noninvasive study of tumor function will make it a very important clinical and research tool in oncology. Recently, whole body PET techniques have been developed which permit imaging of the entire body during a single scanning session promising both in determining the nature of a localized lesion and in defining the systemic extent of malignant disease. FDG-PET scan seems valuable in evaluating patients with GTT resistant to chemotherapy with persistent elevation of beta-hCG levels and localizing the site of a viable tumor. We present three cases of FDG-PET scan in patients with metastatic gestational trophoblastic tumor with a brief review of literatures.