Abstract Background: The association between Helicobacter pylori infection and gastric cancer, which remains a major health problem in Japan, is well established. Detecting infected persons by simple testing and administering eradication treatment might be an effective means to prevent gastric cancer. However, when considering mass screening, the economic benefit must be proven. The purpose of this study is to predict the economic benefit of an H. pylori eradication strategy as a method to prevent of gastric cancer. Methods: Using data in the literature and demographic statistics, the number of persons infected with H. pylori, the infection rate, and the number of those who developed gastric cancer by H. pylori were estimated. Then, a cost benefit analysis of H. pylori screening and eradication treatment was done by using data from the patient survey, basic survey on wage structure, and list of medical fees. The costs are those of screening and eradication treatment, and the benefits are fees that would otherwise have been used for the treatment of gastric cancer, time lost that would have been from work, and the economic loss due to premature death caused by gastric cancer. Results: The infection rates at 10-19, 40-49 and 60-69 years of age were 2.5%, 28.1% and 52.6%, respectively for the year 2010, and the total number of infected persons was estimated to be 37.3 million (29.1% of the whole population). The number of persons who would be at risk of gastric cancer during their lives due to H. pylori infection was 750,000 when we assumed 2% as the risk of gastric cancer by H. pylori infection. The numbers of infected people in 2020, 2030 and 2050 were projected to be 31.3 million, 24.5 million and 11.0 million, respectively. The numbers of persons who would be at risk of gastric cancer due to the H. pylori infection in 2020, 2030 and 2050 would be 630,000, 490,000 and 220,000, respectively. When the subjects of screening and eradication treatment are assumed to be from 16 to 39 years old, and when the response rates of screening and eradication treatment are set at 30% and 60%, respectively, the cost in 2010 would be $841 million. In the case of 20% and 40%, the cost would be $469 million. In the case of 40% and 70%, it would be $1.19 billion. However, the benefit would be $778 million, since the total fee for the treatment of gastric cancer would be $91 million and the loss of profits $686 million. Therefore, the cost benefit ratios would be 0.9, 1.6 and 0.7, respectively. When the response rates of screening and eradication treatment are low, the cost is at a reasonable level but requires more time to be recovered. When the response rates are high, the cost is huge but is recovered very quickly. Conclusions: The infection rate of H. pylori is gradually decreasing in younger people and it is necessary to consider the trend in the number of the infected people, the response rates of screening and that of eradication treatment for the economic evaluation. Citation Format: Nobuo Koinuma. Economic benefit of Helicobacter pylori screening and eradication treatment for the prevention of gastric cancer. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr A05.