OBJECTIVE: To assess whether clinical and/or laboratory-confirmed diagnosis of maternal influenza during pregnancy increases the risk of seizures in early childhood. DESIGN: Analysis of prospectively collected registry data for children born between 2009 and 2013 in three high-income countries. We used Cox regression to estimate country-level adjusted HRs (aHRs); fixed-effects meta-analyses were used to pool adjusted estimates. SETTING: Population-based. PARTICIPANTS: 1 360 629 children born between 1 January 2009 and 31 December 2013 in Norway, Australia (New South Wales) and Canada (Ontario). EXPOSURE: Clinical and/or laboratory-confirmed diagnosis of maternal influenza infection during pregnancy. MAIN OUTCOME MEASURES: We extracted data on recorded seizure diagnosis in secondary/specialist healthcare between birth and up to 7 years of age; additional analyses were performed for the specific seizure outcomes 'epilepsy' and 'febrile seizures'. RESULTS: Among 1 360 629 children in the study population, 14 280 (1.0%) were exposed to maternal influenza in utero. Exposed children were at increased risk of seizures (aHR 1.17, 95% CI 1.07 to 1.28), and also febrile seizures (aHR 1.20, 95% CI 1.07 to 1.34). There was no strong evidence of an increased risk of epilepsy (aHR 1.07, 95% CI 0.81 to 1.41). Risk estimates for seizures were higher after influenza infection during the second and third trimester than for first trimester. CONCLUSIONS: In this large international study, prenatal exposure to influenza infection was associated with increased risk of childhood seizures.