We performed this study to explore the diagnostic accuracies and cutoff values of contrast-enhanced computed tomography (CT) and magnetic resonance imaging (MRI) for the detection and diagnosis of metastatic retropharyngeal lymph nodes (RLNs) in patients with nasopharyngeal carcinoma (NPC). One hundred and twenty-eight patients with a total of 159 RLNs were included in the study. The sizes of maximal and minimal axial diameters of each node on both contrast-enhanced CT and MRI images were measured. The characteristics of the RLNs (malignant or benign), as well as the survival of patients, were classified based on the results of follow-up MRI. RLN size cutoffs of 4-11 mm for minimal axial diameter were used. We found that MRI showed higher sensitivity while CT demonstrated higher specificity. The reasonable criterion for the diagnosis of metastatic RLNs in MRI was a minimal axial diameter of ≥6 mm, which yielded a sensitivity, specificity and diagnostic odds ratio (DOR) of 0.71, 0.82 and 10.88. The radiologic criteria that should be used for the assessment of RLN metastases in NPC patients are nodes with a minimal axial diameter of ≥6 mm on MR images. © 2020 Chen et al.