The spiral bacterium Helicobacter pylori has gained increasing interest as an important gastroduodenal pathogen since its isolation from the gastric mucosa. The presence of Helicobacter pylori in the human stomach is closely associated with chronic gastric inflammatory disease and growing evidence suggests an aetiologic role of this organism in peptic disease. Moreover, epidemiological and histological studies suggest that Helicobacter pylori may be a risk factor for gastric carcinoma and primary gastric lymphoma. Evidence supporting the role of Helicobacter pylori in the pathogenesis of pre-cancerous lesions are reviewed here.