Objective: To make a clinical evaluation of the association between Helicobacter pylori and the occurrence of gastric cancer. Design: Rates of H. pylori infection were assessed in relation to histologically identified atrophic changes in the background mucosa of patients with early gastric cancer, chronic gastric ulcer, atrophic gastritis or a normal stomach. Results: No difference was observed in the rate of H. pylori infection between well and poorly differentiated types of early gastric cancer. Of 41 early gastric cancer cases 61% were H. pylori-positive, a significantly higher rate than in normal controls, the same level as in atrophic gastritis cases but lower than in chronic gastric ulcer cases. H. pylori was frequently detected in the background mucosa in cases with atrophic changes, either with or without intestinal metaplasia, in all groups. There was no difference in the rate of H. pylori infection between three histological types of intestinal metaplasia. Conclusion: It appears that the relationship between H. pylori infection and gastric cancer is indirect and is associated with atrophic processes in the background mucosa.