Chronic gastritis may favour the development of gastric cancer more as a condition than as precancerous lesion. Since, in most cases, it is pathologically correlated with Helicobacter pylori infection, it is reasonable to postulate at least an indirect role for this organism in the pathogenesis of gastric cancer. H. pylori, however, is only one of the risk factors involved, in that additional factors (excess salt, cigarette smoking, deficiency of foodstuffs with an antioxidizing effect) may facilitate the malignant transformation of chronic atrophic gastritis into intestinal-type gastric cancer. Gastric carcinogenesis therefore presents itself as a multifactorial, multistage process, furthered by the occurrence of precancerous lesions which are usually interrelated (type-III intestinal metaplasia, severe dysplasia) and by functional alterations such as achlorhydria, which, though it is not enough in itself to cause gastric cancer, promotes abnormal intragastric bacterial development, a condition which may be followed by abnormal intragastric formation of cancerogenous nitroso compounds. The existence of a close correlation between both gastric cancer and H. pylori infection and low socio-economic and hygienic status of the population lends further strength to the hypothesis that an "H. pylori factor" is involved in gastric carcinogenesis. Consequently, to reduce the risk of gastric cancer, various strategies have been devised to prevent H. pylori infection (improvement in socio-environmental conditions, anti-H. pylori vaccine) and/or to eradicate the organism (by means of therapeutic regimens including antimicrobial agents, which, however, can be implemented only in patients who have not developed diffuse atrophy and/or dysplasia, in whom H. pylori may no longer be detectable). Definitive proof of the real extent of the relationship between H. pylori and gastric cancer and of the efficacy of therapeutic and preventive measures can be provided only by controlled trials in populations with a high prevalence of chronic non-atrophic gastritis which are difficult to organize.