Helicobacter pylori are Gram negative spiral bacteria that colonize human gastric epithelia. Their association with many gastric diseases, including roles in the pathogenesis of chronic gastritis, peptic ulcers, dyspepsia, MALT and gastric cancer is well known. In addition increasing amounts of evidence indicate that they are associated various extragastric entities such as colon cancer, neurodegenerative diseases, liver diseases, coronary artery disease, hematologic diseases and others. Of these, three hematologic diseases have clear associations with strong evidence: iron defi ciency anemia when there is no other explanation, Vitamin B12 (cobalamin) defi ciency and immune thrombocytopenic purpura. Many pathogenic mechanisms have been proposed for these three disorders, and there are many studies that support these associations. In this article we review the role of Helicobacter pylori and its pathogenetic mechanisms in the development of these three hematologic diseases.