Helicobacter pylori infection causes peptic ulcer disease, gastric adenocarcinoma, gastric lymphoma, and probably nonulcer dyspepsia. Although the prevalence of infection is declining over time, the organism still infects approximately one half of the world's population. Only a minority will ever suffer serious consequences from their infection. This article reviews current knowledge about H. pylori and presents some of the dilemmas surrounding clinical and public health approaches to this widespread pathogen.