PURPOSE: We validate the 7th American Joint Committee on Cancer/Union for International Cancer Control (AJCC/UICC) staging system for gastric cancer and propose a new staging system that reflects the prognostic significances of each of T and N category. METHODS: Data from 5,957 patients who underwent curative gastrectomies from 2000 to 2007 at 4 university hospitals in Daegu Metropolitan city in Korea were analyzed for the validation of the 7th AJCC/UICC staging system for gastric cancer. The hazard ratios of the respective T and N categories were estimated and converted to weightings and summated to make prognostic score (P-score). Homogeneity and stage grouping were determined according to the P-scores. RESULTS: In the 7th AJCC/UICC staging system for gastric cancer, poor discrimination was noted between stages IIB and IIIA (P = 0.152). In addition, heterogeneity in stage IIB (P = 0.021) and a small gap in 5-year survival rates (1.7%) between stages IA and IB were noted. A new proposed staging system was generated on the basis of P-scores and demonstrated more discrimination between stages and more homogeneity within stages. The new staging system reflects the different prognostic impacts of N3a and N3b. CONCLUSION: Several controversial issues of the 7th AJCC/UICC staging system for gastric cancer were reconfirmed in the present analysis. The TNM system based on P-score appears to be more scientifically accurate than the 7th AJCC/UICC staging system for gastric cancer.