Purpose: To evaluate the prognostic value of the restaging system after neoadjuvant chemotherapy (NACT) in patients with advanced-stage nasopharyngeal carcinoma (NPC). Materials and Methods: This study was approved by the clinical research committee and a written informed consent was required before enrolling in the study. Prospectively enrolled were 412 consecutive patients with stage III-IVb NPC treated with NACT followed by concurrent chemotherapy and radiation therapy. Patients were staged before NACT and restaged after NACT. The progression-free survival (PFS) and distant metastasis-free survival (DMFS) were calculated with the Kaplan-Meier method, and differences were compared by using the log-rank test. Results: Post-NACT T classification (PFS, P = .001) and N classification (PFS, P < .001; DMFS, P = .001) resulted in better survival curve separations than pre-NACT T classification and N classification. Patients downstaged from N2N3 to N0N1 disease had a better prognosis than did patients who continued to have N2N3 diseases (3-year PFS, 83.8% vs 66.6%, P = .001; 3-year DMFS, 88.0% vs 78.4%, P = .026). Multivariate analysis revealed that post-NACT T classification (hazard ratio [HR] = 1.67; 95% confidence interval [CI]: 1.18, 2.36; P = .003) and post-NACT N classification (HR = 1.54; 95% CI: 1.17, 2.03; P = .002) were independent prognostic factors for PFS; also, post-NACT N classification (HR = 1.48; 95% CI: 1.05, 2.07; P = .025) was an independent prognostic factor for DMFS. Multivariate analysis in patients with N2N3 disease demonstrated that the N downstaging effects of NACT was the only independent prognostic factor for PFS (HR = 0.48; 95% CI: 0.29, 0.81; P = .006) and DMFS (HR = 0.52; 95% CI: 0.28, 0.97; P = .039). Conclusion: The post-NACT stage is more representative of prognosis than the pre-NACT stage in advanced-stage NPC patients, which suggests that major clinical decisions should be based on the post-NACT stage. (C) RSNA, 2016