Even though Helicobacter pylori infection is an obvious cause of chronic non-atrophic and atrophic gastritis, as well as gastric dysplasia and cancer, several recent controlled intervention trials for the prevention of gastric cancer by H. pylori eradication have yielded disappointing results. They showed that cancer eradication may still appear in relatively high frequency after successful treatment of H. pylori. One explanation for this observation is that H. pylori treatment has less influence in development of gastric cancer in atrophic gastritis than in development of cancers in non-atrophic gastritis, and that eradication does not prevent the progression of precancerous lesions and small invisible early cancers to overt tumors. Noteworthy however, the available intervention trials show that gastric cancer can be prevented by H. pylori treatment in patients with non-atrophic gastritis. Trials with higher number of patients, with longer follow-up periods, and with more careful controlling of cancer type and underlying gastric mucosal conditions are needed.