In 1%-2% of head and neck oncology patients, the only symptom of a malignancy is a positive cervical node. The aim of this study was to compare the value of positron emission tomography using fluorine-18 fluoro-2-deoxy- D-glucose (FDG-PET) and conventional diagnostic modalities (CT and/or MRI, panendoscopy) in detecting unknown primary tumours and distant metastases in patients suffering from such a cervical metastasis. Fifty patients (37 men and 13 women) with cervical metastases of an unknown primary tumour were included. All patients underwent FDG-PET. In addition, CT and/or MRI was obtained and panendoscopy was performed. All clinically known metastases were detected by FDG-PET. The primary tumour could be diagnosed in 16 patients (four primary tumours were detected exclusively by FDG-PET). Seven patients had multiple distant metastases, that in six cases were detected exclusively by FDG-PET. The sensitivity and specificity of FDG-PET for detection of unknown primary tumours were 100% and 94%, respectively. For the conventional diagnostic modalities these values were 92% and 76%. FDG-PET had an exclusive effect on the applied therapy in 20% of the patients referred for diagnosis of an unknown primary tumour. The data obtained in this study strongly support the diagnostic strategy of performing FDG-PET in patients suffering from cervical metastases of an unknown primary tumour before any other diagnostic technique.