The prevalence of Helicobacter pylori antibodies increases with age, but it is unknown whether this is due to a constant rate of infection in different age groups, or whether most infection occurs in childhood. Follow-up data on infection rates and the course of infection in an untreated population are scarce. We measured H pylori IgG antibody concentrations in patients who were seen at our endoscopy unit between 1979 and 1983. 115 of 164 eligible patients (70%) participated in the study. H pylori IgG antibody concentrations were measured in two serum samples taken with a mean interval of 11·5 years. 56 patients tested positive at the first visit. During follow-up, 2 patients became infected (annual infection rate 0 30%, 95% Cl 0·04-1·08%). Evidence of infection disappeared in 6 patients: after gastric surgery in 3 and due to an unknown cause in the remaining 3 patients. A non-significant decrease of infection was shown in different age cohorts during follow-up. Antibody concentrations did not increase with age. These results strongly support the concept of dominant infection rates in childhood. Elimination of infection may occur in a few patients without eradication therapy.