The cause of inflammatory bowel disease is still unknown although several bacterial and viral agents have been implicated in their aetiologies. Helicobacter pylori infection, the main cause of gastroduodenal diseases, could, theoretically, be involved in the pathogenesis of inflammatory bowel disease. In fact, it induces permeability alterations and immunological derangements in the stomach similar to those detected in the colon of inflammatory bowel disease patients. However, epidemiological data do not support this hypothesis and recent evidence even points to a low prevalence of Helicobacter pylori in inflammatory bowel disease. These data are discussed in the light of possible confounding factors.