Since the discovery of Helicobacter pylori (H. pylori), numerous studies have considered the possibility that it plays a role in different extragastric diseases. Most of these studies may be classified as epidemiological studies or investigations of H. pylori eradication, but there are also case reports and in vitro studies. This review reveals the limitations common to most of them. Idiopathic thrombocytopenic purpura is the disease for which the strongest association with H. pylori infection has been shown. Data are also accumulating about the role of H. pylori infection in idiopathic iron deficiency anemia and chronic idiopathic urticaria. Interesting results show that H. pylori infection affects atherosclerosis and is weakly associated with ischemic heart disease and stroke. Moreover, CagA-positive H. pylori strains may play a role in the natural history of atherosclerotic stroke. Recent studies suggest a link between H. pylori and Parkinson's disease. Preliminary data indicate that H. pylori infection impairs gastric ghrelin production and may influence nutritional status. The association between H. pylori infection and other extragastric diseases remains controversial. H. pylori infection may cause extragastric manifestations directly or indirectly, by various mechanisms including atrophic gastritis, the release of inflammatory mediators, molecular mimicry, and systemic immune response. Evidence suggests that anti-H. pylori therapy improves idiopathic thrombocytopenic purpura (significant increase of platelet count in half of the cases), iron-deficiency anemia, and chronic urticaria (30% remission rate), but the data from randomized controlled trials are insufficient to confirm these positive effects.