Helicobacter pylori causes gastric cancer in human and in experimental animals. The link between gastritis and H. pylori is causal. Differences in the incidence of gastric cancer in populations with similar high prevalence of H. pylori infection can be related to the differences in the age of acquisition of chronic atrophic gastritis, which in turn is related to an interaction between environmental factors, especially diet, and H. pylori infection. The low odds ratios reported in epidemiology studies evaluating the relation between gastric cancer and H. pylori infection reflect the high overall prevalence of H. pylori in the population and do not accurately reflect the strength of the association. It is time to stop doing serologic studies to confirm the association of gastric cancer with H. pylori and instead expend our efforts on eliminating the infection and investigating the mechanism(s) and interactions.