Although H. pylori is the strongest known risk factor for gastric cancer, most H. pylori-infected persons tolerate the presence of this organism over an entire lifetime without any adverse effects,and some persons may even derive health benefits from H. pylori. An important goal is to define the factors that determine whether gastric cancer will develop, so that the subset of H. pyloriinfected persons with the highest risk of gastric cancer can be identified and targeted for therapeutic interventions.