The use of FDG-PET imaging in tumour detection is now well established. Many studies have suggested that changes in the uptake of FDG predict tumour response to therapy and that further clinical information regarding tumour grade and proliferative status may also be derived from FDG-uptake scans. More studies are required to verify the role of FDG-PET in patient management. Upregulation of hexokinase and glucose transporters, especially Glut-1, and downregulation of glucose-6-phosphatase are frequently associated with transformation. The extent of these changes has been related to both differentiation and proliferation largely corresponding with FDG-uptake studies.