Treatment of the clinical N0 neck in squamous cell carcinoma (SCC) of oral cavity and oropharynx remains a dilemma. None of the current imaging modalities are able to detect the presence of micrometastases in the lymph nodes of clinical N0 necks reliably. The aim of this study was to determine the diagnostic properties of fluorine-18 fluorodeoxyglucose positron emission tomography (FDG PET) in patients clinically staged as N0. FDG PET results of 38 patients were compared to histologic specimens obtained with neck dissections or to follow-up. FDG PET performance was compared to computed tomography (CT), magnetic resonance imaging (MRI) or ultrasonography-guided fine needle aspiration cytology (USgFNAC). Sensitivity and specificity of FDG PET in detecting occult cervical metastases were 50% and 97% respectively. Although FDG PET performed better than conventional imaging modalities, sensitivity was lower than desired. As a consequence, clinical application of FDG PET in the patient staged as N0 is limited.