Purpose To investigate the prognostic significance of standardized uptake value (SUV) of metastatic neck lymph nodes measured on FDG PET/CT in patients with stage IV oro/hypopharyngeal cancers treated by definitive chemoradiotherapy (CCRT). Methods Retrospective analysis of 65 patients with clinically N+ stage IV SCC of the oro/hypopharyngeal squamous cell carcinoma (SCC) who underwent FDG PET/CT scans for primary staging. Follow-up continued till death or at least 24 months from the start of treatment. The primary study endpoint was neck control (NC). The log-rank test and Cox proportional hazard analysis were used to identify significant prognostic factors. Results The 3-year NC rate was 53%. In univariate analysis, N3 status and nodal SUV ≥ 9.8 were significantly associated with reduced NC. In multivariable analyses, nodal SUV retained its independent prognostic significance as a predictor of NC. Lymph node stage was an independent predictor of disease specific survival (DSS). A prognostic scoring system was constructed as follows: score 0 = N0-N2 and nodal SUV 9.8; score 1 = N3 or nodal SUV ≥ 9.8; and score 2 = N3 and nodal SUV ≥ 9.8. Patients with a score of 2 showed the worst NC (hazard ratio [HR], 95% confidence interval [CI]= 10.5, 3.3-33.1; P 0.001) and the lowest DSS (HR, 95% CI = 6.4, 2.2-18.7; P = 0.001). Conclusion The combination of high nodal SUV and N3 neck disease identifies a subgroup of high-risk stage IV oro/hypopharyngeal SCC patients. Further prospective studies are warranted to validate this finding.