The bacterium Helicobacter pylori (H. pylori), prime causal agent of gastroduodenal diseases, has been involved in various aspects of several extragastric manifestations. Although currently available data do not provide proof of its role in most of them, a potential relationship cannot be ruled out. In the present review, the consistency of a role of H. pylori infection in the pathogenesis of diabetes mellitus (DM) as well as in the gastric abnormalities of diabetics is analyzed and critically discussed. Several controversies emerge from the epidemiological data. The clinical consequence of H. pylori infection in terms of metabolic control seems to be low. Regarding interventional studies, the bacterial eradication rate is significantly lower in DM patients than in controls. The difference in the eradication rate observed between adults and children affected by diabetes could be due to the fact that the latter have no history of repeated infectious diseases and antibiotic treatments, with minor antibiotic-resistant H. pylori strain selection. Finally, a higher H. pylori re-infection rate in DM patients than in general population has been shown.