Purpose We assessed the prognostic value of metabolic tumor volume (MTV) measured using$^{18}F$-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) inpatients with locally advanced head and neck squamous cell carcinoma (HNSCC). $Methods$ We retrospectively reviewed 56 patients (51 men, five women; mean age $56.0{pm}8.8$years) who had locally advanced HNSCC and underwent FDG PET/CT for initial evaluation. All patients had surgical resection and radiotherapy with or without concurrent chemotherapy. The peak standardized uptake value ($SUV_{peak}$) and MTV of the target lesion, including primary HNSCC andmetastatic cervical lymph nodes, were measured from FDG PET/CT images. We compared $SUV_{peak}$, MTV, and clinicopathologic variables such as age, Eastern Cooperative Oncology Group (ECOG) performance status, pN stage, pT stage, TNM stage, histologic grade and treatment modality to disease-free survival (DFS) and overall survival (OS). Results On the initial FDG PET/CT scans, the median $SUV_{peak}$ was 7.8 (range, 1.8-19.0) and MTV was17.0 $cm^3$ (range, 0.1-131.0 $cm^3$). The estimated 2-year DFS and OS rates were 67.2% and 81.8%. The cutoff points of $SUV_{peak}$ 6.2 and MTV 20.7 $cm^3$ were the best discriminative values for predicting clinical outcome. MTV and ECOG performance status were significantly related to DFS and OS on univariate and multivariate analyses (p<0.05). Conclusion The MTV obtained from initial FDG PET/CT scan is a significant prognostic factor for disease recurrence and mortality in locally advanced HNSCC treated with surgery and radiotherapy with or without chemotherapy.