Helicobacter pylori is a gram-negative helical-shaped bacterium containing several (usually up to six) twigs. It lives in conditions of low oxygen availability, mainly on the surface of epithelial cells in the pre-pyloric mucosa of the stomach and duodenum. H. pylori is responsible for approximately 80% of gastric ulcers and 90% of duodenal ulcers. It is estimated that in Poland about 84% of adults and about 32% of people under 18 are infected, but most infected people do not develop the disease. The usual route of infection is still controversial. The oral-oral or faecal-oral route are considered as occurring the most frequently.