Helicobacter pylori infection is one of the most common chronic bacterial infection worldwide. Two different epidemiological patterns can be distinguished: one concerning the industrialized countries where an increased prevalence of infection with age is noted and the other found in the developing countries where the majority of young people are already infected when they reach adulthood, the prevalence ranging from 60 to 90% in all age groups. Poland, like most of the Eastern European countries, represents an overall infection rate of 73% and the infection rate for the subjects over 25 years of age of 85-95%. The infection rate observed in the developed countries reflects a so called cohort effect, i.e., a change in the incidence of infection according to generation or age cohort due to changes in socioeconomic conditions. The infection rate observed in the developing countries is mainly determined by a high rate of incidence of this infection in childhood. The risk factors of H. pylori infection are linked to living conditions during childhood, especially to a low socio-economic level of the family including promiscuity. The available data strongly suggest person-to-person transmission of the infection but no agreement has been reached so far whether the oral-oral or faecal-oral route predominates. The incidence of new infections in adults is low, no exceeding 0.5-1.0 per year in the developed countries. One of the greatest risk of infection in adulthood seems to be professional exposure. Studies in industrialized countries show an increase risk of infection among endoscopists with the probability of infection correlating positively with the number of endoscopies performed. In Poland, the medical staff presents a lower seroprevalence (70%) than the general population, however, this prevalence is higher in endoscopists (75%) than in non-endoscopists (59%).