OBJECTIVE: To compare the developmental and behavioral outcomes of children experiencing an initial vaccine-proximate (VP) febrile seizure (FS) to those having a non-VP-FS (NVP-FS) and controls who have not had a seizure. METHODS: In this prospective multicenter cohort study, children with their first FS before 30 months of age between May 2013 and April 2016 were recruited from 4 Australian pediatric hospitals and classified as having VP-FS or NVP-FS. Similar-aged children with no seizure history were recruited as controls. The Bayley Scales of Infant and Toddler Development, Third Edition (Bayley-III) was administered to participants with FS 12 to 24 months after their initial FS and to controls 12 to 42 months of age at the time of assessment. The primary outcome was the Bayley-III cognitive score. Children's preacademic skills were assessed with the Woodcock-Johnson Tests of Achievement, Third Edition, and their behavior and executive functioning were obtained from parent questionnaires. RESULTS: There was no significant difference in cognitive function between children with VP-FS (n = 62), those with NVP-FS (n = 70), and controls (n = 90) (F2,219 = 2.645, p = 0.07). There were no differences between the groups for all other measures and no increased risk of borderline/significant impairment or behavior in the clinical range in children with VP-FS compared to those with NVP-FS or controls. CONCLUSION: VP-FS was not associated with an increased risk of developmental or behavioral problems in young children compared to children with NVP-FS or controls. Parents and providers should be reassured by the absence of adverse effects of VP-FS on the development of children.