Maximum tumor diameter (MTD) is considered by many authors as an important prognostic factor in gastric cancer and, in some series, is reported to be strongly correlated with depth of infiltration. Aim of this study was to evaluate the prognostic value of tumor diameter in a monoistitutional series of 153 gastric cancer patients. The Spearman correlation coefficient was also calculated between MTD and other known prognostic factors. For statistical analysis, patients were grouped as follows: MTD 1, < or = 40 mm, and MTD2, > 40 mm. In our series, MTD resulted significantly linked to survival at univariate analysis (p = 0.0001), but multivariate analysis did not evidence MTD as an independent prognostic indicator. The Spearman correlation test documented that MTD2 is strongly correlated with tumor depth (pT), nodal status (pN) and p-stage (p < 0.01) and is a good predictor of locally advanced stage. This retrospective study showed that patients with larger tumor are at an increased risk for tumor advancement and, therefore, MTD could represent a useful parameter for choosing the most appropriate therapeutic strategy.