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Introduction: The recently published 7th edition of the American Joint Committee on Cancer (AJCC) TNM staging criteria for gastric adenocarcinoma contains some important changes including a re-classification of tumor depth (T) and lymph node (N) status; it also marks the introduction of new stages IIA, IIB and IIIC as well as reclassification of stage IV as patients with distant metastases only. The goal of this study was to validate these new staging criteria in a national population registry and compare it to the prior staging in terms of survival discrimination.Methods: A retrospective review of all gastric cancer patients from Surveillance, Epidemiology and End Results (SEER) registry data from 2004 to 2007 was conducted. The same dataset was used to stage patients according to both 6th and 7th edition criteria. Three-year disease-specific survival was compared using Cox proportional regression.Results: A total of 13,547 patients with gastric adenocarcinoma were identified; 8193 patients (60%) underwent surgery, and 3486 (26%) received radiation therapy. The mean patient age was 66 years. There was a marked increase in the number of patients classified as stage III using the updated criteria (23% vs. 13%), coupled with a decrease in the number of patients classified as stage IV (47% vs. 53%).Re-staging the same patient population according to the 7th edition criteria improved survival discrimination from the 6th edition staging [Figures 1 and 2]. On Cox regression multivariate analysis, significant variables predicting poor survival included high tumor grade (HR 1.17, CI: 1.10-1.26; p<0.001) and distal location of primary tumor vs. proximal location (HR 1.78, CI: 1.64-1.93; p<0.001). Hazard ratios by stage (vs. stage IA) showed linear progression and a statistically significant survival difference from the prior stage: Stage IB, 2.16 (CI: 1.56-2.98); IIA, 3.25 (CI: 2.44-4.32); IIB, 6.14 (CI: 4.70-8.02); IIIA, 8.76 (CI: 6.75-11.4); IIIB, 11.8 (CI: 9.20-15.2); IIIC, 16.7 (CI: 13.0-21.5); and stage IV, 20.2 (CI: 15.9-25.8) (all p<0.001). Conclusions: The AJCC 7th edition staging criteria demonstrates better survival discrimination than previous criteria. A smaller proportion of patients were classified as stage IV using the updated criteria, with 13% of stage IV patients down-staged to IIIC. The revisions reflect better prognosis and allow for more appropriate selection of therapeutic options, of particular importance in the modern era of multi-modality therapy. Our study therefore validates the recent revisions made to the T and N stages in the 7th edition AJCC staging criteria for gastric adenocarcinoma.