Helicobacter pylori is a cause of gastric adenocarcinoma, but the role of H. pylori eradication in reducing cancer risk is unknown. We sought to estimate the benefits of a screening and treatment programme for H. pylori infection, aimed at reducing the incidence of gastric cancer in Australia. The impact of this programme on cancer incidence was evaluated in sensitivity analyses utilizing Western Australian Cancer Registry data and published data on the epidemiology of H. pylori and gastric cancer. The impact of variation in parameters used in the sensitivity analyses was substantial, ranging from a 38% reduction in lifetime risk of gastric cancer in a best-case to 3% in a worst-case scenario. In an intermediate-case scenario there is a 23% reduction in lifetime risk, but in real terms this reflects a fall in cumulative incidence from 0.7 to 0.5% for males or 0.3 to 0.2% for females. The projected cumulative lifetime incidence of gastric cancer in H. pylori-infected males is 2.2% and 0.9% for females; this contrasts with 0.4 and 0.2%, respectively, for those never infected. According to an intermediate-case scenario, to prevent one gastric cancer, screening with or without subsequent treatment would be required in 617 men or 1639 women. Furthermore, this programme may be less effective in reducing cancer incidence than would be achieved naturally over the next 15 years, providing the current annual decline in gastric cancer incidence continues. In conclusion, the benefits of a community based programme of H. pylori eradication in terms of cancer risk reduction remain unclear, related largely to uncertainties in the parameters used to calculate these benefits. In Australia, any benefits obtained are likely to be, at best, modest.