In order to avoid confusion in categorizing malignant lesions for surgical treatment, a definition and criteria of carcinomas significantly involving the esophagogastric junction (ECJ-Ca) and those of gastric cardia less significantly involving the esophagogastric junction (eC-Ca) are proposed, devised as this study was from a practical viewpoint. A comparative analysis of carcinomas of these groups was carried out, the control group being those carcinomas situated mainly in the upper third segment of the stomach but not involving the esophagogastric junction (C-Ca). Carcinomas of these regions can be determined by the EGJ-Index (EGJ-I) calculated through the following formula: EGJ-Index = [( Length of the esophageal portion of the lesions)/(length of the of the esophageal portion + gastric portion of the lesion])x1,000. Thus lesions of these regions are easily and practically classified as follows: [I]: EGJ-Ca 250 less than or equal to EGJ-I less than or equal to 750, 59 cases; ( II]: eC-Ca 0 less than or equal to EGJ-I less than 250, 88 cases; [III]: C-Ca 0 = EGJ-I, 208 cases. We found these categories quite suitable for practical use.