The main indications for Fluoro-deoxyglucose-position-emission tmomography (FDG-PET) in head and neck tumors (HNT) are the primary staging of high-risk patients e.g. Primary Tumur size 2 (3pT2) with an emphasis on the evaluation of lymph node involvement and presence or absence of organ metastases, an assessment of suspected recurrence, the evaluation of local or distant metastases and the search for primary tumors in CUP-syndrome. An ongoing prospective study was conducted covering 124 patients of both sexes between the ages of 34-72 years. Fifty-six patients were suspected of recurrence, 53 patients showed a staging due to large primary and patients with CUP-syndrome. Primary tumour localizations showed a majority of oropharynx (n=55) followed by larynx (n=20), hypopharynx (n=10), etc. Histologically most cancers were squamous cell carcinoma. In this study in 27% of patients with CUP syndrome, FDG-PET could identify the primary tumour whereas CI has failed. The data of this study as well as previous investigations indicate FDG-PET as a valuable diagnostic tool in the assessment and therapy management of head and neck tumors. FDG-PET exerts a reproducible high sensitivity and accuracy under clinical routine conditions within an appropriate selected patient cohort. Qualitative image assessment employing reference organs seems to be sufficient for reliable interpretation of FDG-positive lesions. Due to the high glucose utilization of HNT it is possible to delimit even small processes of >5-7 mm, although micrometastases <5-7 mm could not be detected.