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.