Although a screening program for gastric cancer, using barium X-ray examination, has been carried out widely in Japan for the past 3 decades, there is insufficient evidence to confirm its effectiveness in terms of reducing mortality. To evaluate the effectiveness of the screening, a population-based case-control study was carried out in Miyagi Prefecture, Japan. Case subjects, who had died from gastric cancer (198) and control subjects matched in age, sex and residence (577) were selected from among members of the National Health Insurance. Their screening histories during 5 years before the cases were diagnosed were surveyed on the basis of records of the regional cancer registry and the cancer-detection center. The odds ratio (OR) of death from gastric cancer for the persons who participated in the screening at least once during 5 years was 0.41. For those who participated only once during 5 years the OR was 0.43, and for those whose last participation was 5 years earlier it was 0.30. Our data suggest that screening for gastric cancer at 5-year intervals might reduce mortality by 60%, and that the effect might remain for at least 5 years.