Acquisition of H. pylori infection occurs typically in childhood and the incidence is very low among persons over 20 years of age. Prevalence of H. pylori infection in a particular birth cohort is determined by the risk for acquisition of the infection during childhood. Prevalence of the infection remains generally unchanged during adulthood, while each birth cohort has a characteristic prevalence rate. In developed countries, a vast majority of adults are infected with H. pylori. In industrialized countries, the prevalence of H. pylori infection has significantly decreased in younger cohorts, probably due to better living conditions and improved hygiene, and possibly also due to changed dietary habits and nutritional status. In Estonia, the prevalence of H. pylori infection has been very high, however, since 1991, the prevalence of the infection in children has decreased significantly. Spontaneous elimination of H. pylori infection at the population level can be so rapid that it is comparable to the effect of widely applied anti-H. pylori treatment. Decreasing prevalence of H. pylori infection is accompanied by decrease in the incidence of peptic ulcer and gastric cancer.