The prevalence of Helicobacter pylori in children ranges from 10% to more than 80%. High prevalence occurs in developing countries, and after colonization it takes an extended period to be eradicated by the immune system. To evaluate the prevalence and age distribution of H. pylori infection in children in Shiraz (a city in the south of Iran), we collected 593 stool samples from children selected randomly from 5 age groups. Infection was determined based on antigen immunoassay in stool using the enzyme-linked immunosorbent assay method. The prevalence rates were 82%, 98%, 88%, 89%, and 57% in age groups of 9 months, and 2, 6, 10, and 15 years, respectively. There were no significant differences between the prevalence of H. pylori infection in the first 4 age groups (P > 0.05), but there was a significant decrease in the 15-year-old group (P < 0.05). The prevalence of H. pylori infection in the south of Iran is very high. The infection begins at infancy and remains high until late childhood.