OBJECTIVE Helicobacter pylori infection is recognized as being strongly associated with chronic gastritis, duodenal ulceration and probably gastric carcinoma. Seroepidemiological studies have shown that a large proportion of healthy people have antibodies against H. pylori. A serological study was conducted in an asymptomatic Turkish population to investigate the seropositivity rate of H. pylori and to detect the relationship with age. METHODS A total of 657 serum samples collected from 331 male and 326 female people in different age groups who had no gastrointestinal complaints were studied by a commercial ELISA test for the presence of H. pylori-IgG antibodies. RESULTS Three hundred and forty-eight subjects (53%) were seropositive. The overall seropositivity rates did not differ with sex. Antibody prevalence increased progressively with age. The seropositivity rates were as follows: 17.4% < 1 year old; 15.5% aged 1-4; 30.6% aged 5-9; 47.3% aged 10-14; 58.4% aged 15-19; 62.6% aged 20-29; 67.6% aged 30-39; 81.3% aged 40-49; and 66.3% over 50 years of age. CONCLUSIONS This study indicated that more than 30% of the subjects acquired infection before teenage and that about 70% of adults had antibodies against H. pylori in our population. The high prevalence and early acquisition of H. pylori infection may be related in part to socioeconomic status and traditional living conditions in Turkey.