The fusion of 18-fluorodeoxyglucose (FDG) positron-emission tomography (PET) with computed tomography (CT) offers both anatomic and physiologic delineation of head and neck cancers. PET-CT is useful in the staging of head and neck carcinomas and may identify unsuspected distant metastasis that may alter treatment. PET-CT may also help in target volume delineation during radiotherapy (RT) treatment planning. Better characterization of the target may improve local control as well as spare normal tissues from RT sequelae.