(18)F-Fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET)/CT imaging of squamous cell carcinoma of the head and neck (HNSCC) renders the possibility to study metabolic tumor activity by measuring FDG-uptake expressed as maximum standardized uptake value (SUV(max)). A correlation between SUV(max) and several factors including T-classification, histological tumor differentiation or different anatomic subsites is of potential interest in HNSCC. The aim of this study was to evaluate how metabolic tumor activity derived from FDG-PET correlates with prognostic clinical and pathological parameters including these factors. 262 patients with HNSCC undergoing PET/CT for initial staging were assessed separately for a potential correlation between SUV(max) and T-classification, histological grading, and anatomical subsites of the primary tumor. Nonparametric testing showed a significant correlation between SUV(max) and T-classification (P < 0.001). On the contrary, no statistically significant correlation was found between SUV(max) and histological tumor grading. Furthermore, no statistical significant correlation between the different anatomical subsites and SUV(max) were found. There was no significant correlation of SUV(max) and tumor grading after adjustment for T-stage and anatomical localization of the tumor, neither. Conclusion: Metabolic tumor activity correlates with T-stage of HNSCC. However, histological tumor grading does not correlate with SUV(max). The role of primary tumor SUV(max) as a predictor of outcome or survival remains unclear. Clinicians should therefore exercise caution in attributing any clinical importance to SUV(max) obtained from a single PET/CT exam.