We analyzed the rate of occurrence of gastric cancer in a population of 39,250 by mass screening survey. In 0.123% of the total subjects gastric cancer was detected, 0.064% was at early stage and 0.059% at an advanced stage. The incidence of gastric cancer in the newly examined persons was 0.17%, 0.08% was at early stage and 0.09% at advanced stage. Of the frequently examined persons 0.07% was found to have gastric cancer, 0.043% at early stage and 0.027% at an advanced stage. The rate of occurrence of early gastric cancer was significantly higher than that of advanced gastric cancer within a 1 1/2 year interval of screening. From these results, gastric mass screening survey is considered to be effective in detecting asymptomatic gastric cancer in the "newly examined persons," and also to be beneficial in detecting "early" gastric cancer at intervals of 1 1/2 years of screening.