There are geographic and ethnic differences in gastric cancer incidence around the world, as well as trends in each population over time. Incidence patterns observed in immigrant group changed in relation to the countries they lived in. All of these factors serve to indicate the close association of gastric cancer with modifiable factors. Infection with Helicobacter pylori is a strong and established risk factor for gastric cancer, but is not a sufficient cause for its development. Substantial evidence strongly suggests that the risk may increase with smoking and a high intake of salted foods, and decrease with a higher intake of fruits and vegetables. Therefore lifestyle modification represents a practical strategy to prevent gastric cancer among middle aged-to-elderly Japanese, most of who are infected with Helicobacter pylori.