Because gastric cancer is still the most common cancer, its prevention is one of the most important aspects of Japan's cancer control strategy. Observations among Japanese immigrants in the USA and Brazil based on the geographic differences, the trend in cancer incidence with time, and the change in incidence patterns indicate that gastric cancer is closely associated with dietary factors, such as the intake of salt and salted food. In international and intra-Japanese ecological studies, the average salt excretion level, estimated using randomly selected 24-h urine samples in each population, was closely correlated with gastric cancer mortality. Several case-control and cohort studies, including the author's recent works, have shown that a higher intake of some traditional salt-preserved food and salt per se, which was estimated using a validated food-frequency questionnaire, was associated with a risk of gastric cancer. While salted food intake may increase the risk of Helicobacter pylori infection, it can also act synergistically to promote the development of gastric cancer. Based on substantial evidence about the association between salt and salted food intake and the risk of gastric cancer from ecological, case-control, and cohort studies conducted in Japan and other countries, as well as mechanistic plausibility, dietary modification involving less salt and salted food intake is a practical strategy with which to prevent gastric cancer.