Background Since the eighth American Joint Committee on Cancer (AJCC) classification recently introduced the clinical classification for preoperative staging of gastric cancer, the new clinical classification has not been extensively validated yet. Therefore, in this study, we compared the prognostic performance of the new clinical classification and the pathologic classification for preoperative staging of gastric cancer. Methods We reviewed 3027 patients with gastric cancer who were surgically treated between 2009 and 2013. Patient survival was analyzed according to the preoperative stage by the clinical classification and the pathologic classification in the eighth AJCC classification. The prognostic performance was examined using the Akaike information criterion (AIC) value and Harrell c -index. Results Patient survival was significantly different across the different stages when both classifications were used. However, individual pairwise comparisons showed that survival differences between each stage were more distinctive and homogeneous in the pathologic classification. In the multivariate model adjusted for the final pathologic stage, preoperative staging by the pathologic classification was an independent prognostic factor, whereas the clinical classification was not. The pathologic classification showed a lower AIC value compared with the clinical classification (5100.64 vs. 5114.14). The Harrell c -index was higher in the pathologic classification than in the clinical classification (0.741 vs. 0.739). Conclusions The new clinical classification in the eighth AJCC classification discriminates patient survival well. However, it does not appear to have a better prognostic performance compared with the pathologic classification for preoperative staging of gastric cancer.