The problem of diagnosis in the field of head and neck region is still valid. Specific diagnosis and precise estimation of the tumor's size with the use of CT and MRI imaging is generally unsatisfactory. The Positron Emission Tomography (PET) supports this process with additional information about the tumor's metabolism. Numerous publications show that PET-CT has a great influence on the evaluation of the size of the tumor, presence of lymph node metastases, choice of treatment and the prognosis of the recurrence. Cancer cells represent a specific metabolic state. These cells intake large quantities of glucose and utilize it in the process of glycolysis. The oxidative phosphorylation is not efficient in the transformed cells and defects in mitochondrial functions are at the heart of malignant cell transformation. Disruption of the oxidative phosphorylation chain has been described in the neoplasms. As a consequence, in cancer the glycolysis is active even in the normoxic environment. This metabolic shift in cell transformation has been described in early XX century and so called Warburg's hypothesis profoundly influenced the present perception of cancer metabolism, positioning what is termed aerobic glycolysis in the mainstream of clinical oncology. Today we know that neoplastic cells differ at the proteomic level. A subset of different proteins such as hexokinase II or HIF are upregulated. These abnormalities might be used as the neoplastic markers.