ObjectivePrevious clinical studies in adults from developed countries have implicated Helicobacter pylori infections in the development of thrombocytopenia. However, studies in children, particularly those from low-income countries, are unusually scarce. We examined the association between H. pylori infection and platelet indices in young Ethiopian school children.DesignCross-sectional studySettingThis study was conducted in five elementary schools located in central Ethiopia.ParticipantsBlood and stool samples were collected from 971 children across five elementary schools in Ethiopia. H. pylori infection was diagnosed using stool antigen and serum antibody tests, and haematological parameters were measured using an automated haematological analyser. An interviewer-led questionnaire administered to mothers provided information on demographic and lifestyle variables. The independent effects of H. pylori infection on platelet indices were determined using multivariate linear and logistic regressions.Study outcomesH. pylori-infected children had a lower average platelet count and mean platelet volume than uninfected after adjusting the potential confounders (adjusted mean difference: −20.80×109/L; 95% CI −33.51 to −8.09×109, p=0.001 and adjusted mean difference: −0.236 fL; 95% CI −0.408 to −0.065, p=0.007, respectively). Additionally, H. pylori-infected children had lower red blood cell counts (adjusted mean difference: −0.118×1012/L; 95% CI −0.200 to −0.036, p=0.005) compared with non-infected.ConclusionOur study from a developing country provides further support for an association between H. pylori infections and reduced platelet indices in young Ethiopian school children, after controlling for potential confounders. Further research is needed, particularly longitudinal studies, to establish causality.