ObjectivesChildren from South Asian ethnic backgrounds are at increased risk of obesity and its associated future health risks; however, evidence is lacking as to whether parental concern about their child’s future overweight risk varies by ethnic background. We hypothesised that parents of 5-year-old children from South Asian backgrounds would be more likely to express such concerns.DesignCross-sectional.SettingUK.Participants15 039 singleton 5-year-old Millennium Cohort Study participants (48.9% girls; 86.7% White).Primary outcome measureParent-reported concern (some/none) about future overweight risk.MethodsWe estimated the adjusted ORs (aORs) of some parental concern (ranging from a little to very concerned) by child’s ethnic background (reference group: White), adjusted for parent and child weight status, and child sex.ResultsParents of girls from Pakistani (aOR 0.4; 95% CI 0.2 to 0.5), Bangladeshi (0.3; 0.2 to 0.5), Black African (0.5; 0.3 to 0.7) and Mixed (0.7; 0.5 to 0.99) ethnic backgrounds and of boys from Pakistani ethnic backgrounds (0.6; 0.4 to 0.9) were less likely to report concern about their child’s future overweight risk than parents of White girls and boys, respectively. Overweight (2.5; 2.2 to 2.8) and obesity (6.7; 5.7 to 7.9) in children, and overweight (1.4; 1.2 to 1.5) and obesity (1.9; 1.7 to 2.2) in parents, were associated with increased likelihood of concern.ConclusionsParents of children from South Asian ethnic backgrounds express less concern about their child’s future overweight risk. Qualitative studies are needed to understand the concerns of parents from different ethnic backgrounds to inform weight-management interventions in ethnically diverse populations.