Objective: The presence of metastatic cervical lymph nodes (MCNs) is an unfavorable prognostic factor in head and neck cancer. The total volume of MCNs (MNV) and the lymph node ratio (LNR) may be superior to conventional nodal staging in cervical metastasis from an unknown primary tumor (CUP). We evaluated the prognostic value of MNV and LNR in CUP patients. Methods: Thirty-nine patients with CUP who underwent surgery plus postoperative radiotherapy were reviewed. MNV was measured by preoperative computed tomography and LNR was determined using neck dissection samples. The association of clinicopathologic factors, MNV, and LNR with disease-free survival (DFS) and overall survival (OS) was analyzed. Results: Five-year DFS and OS were 68.4 and 70.8%, respectively, for a median follow-up of 49 months. In multivariate analysis, MNV (>30 ml) was an independent prognostic factor for both DFS and OS (p = 0.004 and p < 0.001, respectively). LNR (>0.14) was identified as an independent predictive factor for DFS (p = 0.041). Conclusion: MNV and LNR are independent prognostic factors in patients with CUP and could facilitate the identification of high-risk patients requiring intensive treatment and surveillance.