In the 15-year period 1970 to 1984, the Detection Center of Hokkaido Cancer Society discovered 2,508 gastric cancer cases (1,681 male, 827 female) including 999 cases of early gastric cancers. The survey included 2.01 million people in Hokkaido. Among the cases, 2,508 were diagnosed as stomach cancer, which amounted to 0.12% of the total screened during the period. The proportion of early gastric cancers has been increased over this period. Of those suffering from gastric cancer, 2,287 cases were operable. Mucosal carcinoma accounted for 479 cases, carcinoma with invasion to submucosa accounted for 520 cases. Early gastric cancer numbered 999 cases, or 43.6% of the operable cases. Advanced cancer or cancer with invasion beyond the muscularis propria totalled 1,288 cases, or 56.4% of the operable cases. The relative survival rate was calculated which shows the survival ratio of detected cancer cases to the general population: 67.8% 5-year, 64.0% 10-year and 63.5% 15-year survival rate. These results show that cancer detection leads to a good relative survival rate. The relative survival rate flattens after five years, because the curve of the survival rate of cancer patients decreases gradually, while the expected survival rate of the general population remains constant. If lead time is not considered, the 5-year relative survival rate is satisfactory: if it is considered, however, the 10- or even 15-year survival rate may well be estimated. The 15-year relative survival rate of surgically treated early gastric cancer, advanced gastric cancer and total cancer are 94.0%, 51.0% and 70.7% respectively. These data clearly show that early gastric cancer treated surgically carries an excellent chance for 15-year survival when compared to advanced cancer. One may also note the relatively high survival rate of 63.5% in all gastric cancer patients discovered by this program; this figure reflects a high proportion of early gastric cancer among all cancers. As presented, the mass screening program does have positive effects in reducing gastric cancer deaths by detecting more early gastric cancer cases than among usual clinic patients.