The development of functional imaging using positron emission tomography (PET) has been a major advancement in clinical oncology. In addition, the integration of functional imaging with CT anatomical imaging (PET-CT) has dramatically increased the clinical applicability of PET. This review discusses the current role of PET-CT in head and neck cancer, focusing on its role in staging, detection of unknown primaries, radiotherapy planning, assessment of treatment response, and biological characterization of disease. We also demonstrate why PET-CT should be an integral part of modern management of head and neck cancer.