This thesis deals with he development of a new method for controling the precision of the first screening in the mass survey for stomach cancer, which obtained the desired result. The method of assuming the false negative case in the first screening by using the Accidentally Detected Cancer in the Close Examination (ADC) was developed, for which was named the ADC method. The mass survey of Hokkaido Anti Cancer Association was the object of this study for the estimation of validity of the ADC method. The precision was investigated according to the year, the location, the size, the type and the depth of invasion of stomach cancer. The object was the mass survey from 1970 to 1976, the total examined reached 777,058 and the number of detected cancer amounted to 991. The false negative rate (FNR) investigated by the ADC method was 28.3%, and the precision rose annually. As for the location, FNR was high in case of the greater curvature, the anterior wall, and the posterior wall. In the small lesion as well as the shallow depth of invasion, FNR was high and so was in elevated type. It seems that these results correspond with the former reports and the common idea, which indicate the validity of the ADC method which was developed. The same kind of FNR in the same object was investigated by using the follow up study which had been the common method for assuming the false negative case, and the ADC method proved to be better compared with that.