Helicobacter pylori (Hp) is the most common chronic bacterial infection in humans worldwide. The prevalence of Hp infection is high in developing countries (80-90%) and lower in developed countries (10-30%). In vast majority of infected individuals, the infection is acquired early in life. The risk of Hp infection is related to low socio-economic status and living conditions at early childhood (density of housing, overcrowding, number of siblings, sharing a bed, and lack of running water, low education of parents). Smoking is a risk factor of Hp infection in adults. In developed countries including the Czech Republic, the overall prevalence of Hp infection has fallen dramatically over recent decades. This decrease can be explained mostly by the relatively favourable and improving socio-economic conditions. However, it is necessary to consider also the fundamental determinants of "modern times" that could cause gradual disappearing of Hp from the human "microbiome".