Helicobacter pylori is one of the most common infections in the world. Despite inciting inflammation, immunological clearance of the pathogen is often incomplete. CD4+CD25hiforkhead box protein 3 (FoxP3+) regulatory T cells (Tregs) are potent suppressors of different types of immune responses and have been implicated in limiting inflammatory responses to H. pylori. Investigating the influence of H. pylori on Treg function and proliferation, we found that H. pylori-stimulated dendritic cells (DCs) induced proliferation in Tregs and impaired their suppressive capability. This effect was mediated by interleukin (IL)-1β produced by H. pylori-stimulated DCs. These data correlated with in-vivo observations in which H. pylori+ gastric mucosa contained more Tregs in active cell division than uninfected stomachs. Inciting local proliferation of Tregs and inhibiting their suppressive function may represent a mechanism for the chronic gastritis and carcinogenesis attributable to H. pylori.