Positron emission tomography (PET) with fluorodeoxyglucose (FDG) allows the visualization of metabolic tissue activity. Use of FDG in in-vivo cancer imaging is based on enhanced glycolysis in tumor cells. In vivo experiments have demonstrated the potential use of FDG PET in squamous-cell head and neck tumors and the detection of tumor involvement in lymph nodes. Since its introduction in this area, several papers have appeared on the use of this imaging modality. Indications for the use of FDG PET in patients with head and neck cancer are discussed.