To investigate the indications of 18F-2-fluoro-2-Deoxy-D-glucose (FDG) Positron Emission Tomography (PET) in head and neck cancer, the present study focuses on a case of cervical metastatic lymph node, which is not detected by the routine approach. It discusses the potential role of FDG-PET in the detection of unknown primary tumors, lymph node metastasis and post radiation follow-up, and demonstrates the implications of its findings through a few examples. Based on the literature in the field of head and neck oncology, the paper recommends the following uses for FDG-PET: 1. To guide biopsy or even local resection at the initial stage of examining the unknown primary lesions in case of high clinical suspicion 2. A whole body PET in high-risk patients may prevent unnecessary treatment and reduce the number of examinations 3. To monitor tumor response before full-dose irradiation so as not to delay the salvage surgery when applicable 4. To detect residual, recurrent or secondary neoplasm after definitive radiotherapy at least 4 months post-treatment 5. To revise the necessity of neck treatment in case of a negative PET, in the NO necks; and 6. In cases of clinical suspicion for laryngeal cancer recurrence and absence of objective findings before obtaining biopsy.