Helicobacter pylori is the aetiological agent of chronic gastritis and a major causative factor in duodenal and gastric peptic ulcer disease; a strong association also exists with gastric cancer and primary gastric lymphoma. The prevalence of infection in adults ranges from less than 15% in developed countries to virtually 100% in less developed areas. If H. pylori infection alone was responsible for the development of gastritis, peptic ulcer disease, gastric carcinoma and primary gastric lymphoma, one would expect the frequency of all these conditions to parallel closely the prevalence of H. pylori infection. This is clearly not the case: therefore, genetic, environmental and cultural factors must act in concert with H. pylori to induce different outcomes of the infection. This paper outlines the geographic approach to the study of disease and discusses the possible application of this methodology to the inquiry into the relationship between H. pylori, atrophic gastritis and gastric cancer. Preliminary results of a study showing great variation in the prevalence of intestinal metaplasia in duodenal ulcer patients from different geographic origin are presented and briefly discussed.