OBJECTIVE The purpose of this study was to evaluate the usefulness of ultrasound (US) volume measurement of the cervical lymph nodes for diagnosing nodal metastasis in patients with head and neck cancer using a node-by-node comparison. METHODS Thirty-four consecutive patients with head and neck cancer from one tertiary university hospital were prospectively enrolled from 2012 to 2017. Patients with histologically proven squamous cell primary tumors in the head and neck region scheduled to undergo a therapeutic neck dissection were eligible. For each patient, 1-4 target lymph nodes were selected from the planned neck dissection levels. Lymph nodes with thickness >20 mm or in a cluster were excluded. Node-by-node comparisons between the pre-operative US assessment, the post-operative actual measurements and histopathological results were performed for all target lymph nodes. Quantitative measurements, such as three diameters, ratios of the three diameters and volume were analyzed in this study. Lymph node volume was calculated using the ellipsoid formula. RESULTS Patients comprised 28 men and 6 women with a mean age of 60.0 years (range, 29-80 years) at the time of surgery. In total, 67 target lymph nodes were analyzed in this study and the thickness ranged from 3.9 to 20.0 mm (mean 8.0 mm). There was a strong correlation between the US volume and post-operative actual volume (ρ = 0.87, p < 0.01). The US volume measured 2156 ± 2156 mm3 for the tumor positive nodes, which was significantly greater than the US volume of 512 ± 315 mm3 for tumor negative nodes (p < 0.01). Significant differences between tumor positive and tumor negative nodes were found in five variables (volume, thickness, major axis, minor axis and ratio of minor axis to thickness) for total lymph nodes. To identify predictors of lymph node metastasis, ROC curves of the US variables of target lymph nodes were compared, of which 4 variables were considered acceptable for predicting the lymph node metastasis: volume (AUC 0.86), thickness (AUC 0.86), major axis (AUC 0.79), and minor axis (AUC 0.79) for total lymph nodes. The optimal cut-off level for US volume in total lymph nodes was found to be 1242 mm3, whereby a 62% sensitivity and 98% specificity was reached (likelihood ratio: 25.2). CONCLUSIONS Pre-operative ultrasonic volume measurement of the cervical lymph nodes was useful for early detection of cervical nodal metastasis in head and neck cancer.