This study aimed to disentangle the independent contributions of Helicobacter pylori infections in mothers, fathers and siblings to the risk for the infection in the 11–13 years age group. Index children from a cross-sectional Stockholm school survey and their family members completed questionnaires and contributed blood samples. H. pylori serostatus was determined with an enzyme-linked immunosorbent assay and immunoblot. Fifty-four seropositive and 108 seronegative index children were included and 480 out of 548 family members contributed blood. In multivariate logistic regression modelling, having an infected mother (OR 11·6, 95% CI 2·0–67·9) or at least one infected sibling (OR 8·1, 95% CI 1·8–37·3) were risk factors for index child infection, whilst the influence of infected fathers was non-significant. Birth in high-prevalence countries was an independent risk factor (OR 10·4, 95% CI 3·4–31·3). H. pylori infections in mothers and siblings and birth in high-prevalence countries stand out as strong markers of infection risk amongst children in Sweden.