The molecular-cellular features of gastric mucosal inflammation caused by Helicobacter pylori are formulated. Chronic gastritis is considered as the morphological basis of gastric ulcer and non-cardial cancer of the stomach of intestinal type. The basic influences of the products of a pathogenicity island of bacterium (Cag A-protein) and VacA-cytotoxin on the gastric mucosa, as well as bacterial genetic polymorphism are discussed. The evolution of the phenotypes of chronic gastritis-- "ulcerative" "cancerous" is analyzed. Helicobacter pylori-associated inflammation may depend on the host's inflammatory response which in turn is determined by the allelic polymorphism of cytokine genes rather than the genetic characteristics of a bacterial strain.