The hybrid technique of PET/CT has significantly impacted the imaging and management of head and neck squamous cell cancer (HNSCC) since its introduction and has become the technique of choice for imaging of this cancer. Diagnostic FDG PET/CT is useful for identification of an unknown primary tumor, delineation of extent of primary tumor, detection of regional lymph node involvement even in a normal-sized node, detection of distant metastases and occasional synchronous primary tumor, assessment of therapy response, and long-term surveillance for recurrence and metastases. The role of PET/CT is evolving in radiation therapy planning. Combined diagnostic PET/CT provides the best anatomic and metabolic in vivo information for the comprehensive management of HNSCC. FDG PET/CT is the modality of choice in detecting metastasis of differentiated thyroid cancer, when the disease is iodine negative. It is valuable in staging and prognosis of anaplastic and medullary thyroid cancer.