This paper will briefly review the evidence for the role of Helicobacter pylori infection in the aetiology of gastric cancer and consider the implications of this relationship. The critical issue of whether H. pylori eradication may play a part in a strategy for the prevention of gastric cancer will then be discussed. Although this paper will largely be concerned with epidemiological evidence, it should be emphasised that an understanding of the mechanistic basis to the H. pylori-cancer relationship is also advancing rapidly and this area will be reviewed in the paper by Correa elsewhere in this issue.