Epidemiologic data are presented about the prevalence of Helicobacter pylori positivity as determined by serology in a large series of asymptomatic children (n = 466). Serology is now generally accepted as a valid noninvasive screening method for the detection of Helicobacter pylori infection. Blood samples were taken from 466 apparently healthy children (ages 2-14 years) who were admitted to our pediatric 1-day clinic for elective surgery. The children originated from different ethnic backgrounds. All were born in Belgium and have been living there ever since. Thirty-four (7.3%) had positive titers for Helicobacter pylori. There was a significant increase in the number of positive patients with advancing age (5.4% in the age group 2-8 years and 13.4% in the age group 8-14 years; p < 0.001). We also found a significant difference in the prevalence of Helicobacter pylori positivity between Caucasian Belgian children and non-Caucasian children of different ethnic backgrounds. This relatively high prevalence of positive serology in asymptomatic older children (13.4%) should be considered in studies on the incidence or causative role of Helicobacter pylori in children with chronic abdominal complaints.