Helicobacter pylori appears to be the most important cause of gastritis and gastric and duodenal ulcer. Its eradication, in fact, promotes healing of these diseases and significantly reduces ulcer recurrence. In the last few years, moreover, besides a local tissue damage, an association between H. pylori infection and various extraintestinal pathologies has also been described. The presence of more toxic strains of H. pylori and the multiplicity of the substances produced, directly or indirectly, in response to the bacterium, besides a genetic predisposition of the individual, are all factors which may enhance the ability of Helicobacter to generate both local and systemic damage.