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Objective. Our goal was to assess development, cognition and behaviour following an initial complex febrile seizure (FS), at onset and school age, in the context of known risk factors for cognitive development.Methods. Two cohorts were recruited. Thirty-five infants with an initial complex FS were assessed within the first year post-seizure and compared to 30 controls (simple FS) based on measures of cognitive, motor and language development, behaviour and emotions. Additionally, 19 school-age children with previous complex FS (11 multiple, eight prolonged) were assessed and compared to 19 controls (simple FS) based on measures of intelligence, learning/memory, executive functioning, behaviour and emotions.Results. Within the first year post-onset, infants with complex FS did not significantly differ from controls based on developmental measures. Seizure duration and age at seizure onset did not impact developmental outcome. School-age children with complex FS showed unaltered global intelligence, but lower executive functioning, compared to controls. Children with prolonged FS also showed evidence of a lower level of learning and memory abilities. Neuropsychological scores correlated with seizure duration. Children with complex FS showed more attentional problems and anxious/depressed symptomatology at onset and school age, and more hyperactivity at school age.Significance. Infants with complex FS seemed to show normal development within the first year post-seizure onset. However, challenges in executive functioning, learning and memory at school age were found in children with a history of FS. Hence, at school age, cognitive challenges cannot be excluded based on undifferentiated early cognitive development, and may occur even in the absence of the most severe form of FS (i.e., FSE). Beyond the limits of this study (i.e., small sample size, use of parental questionnaires for emotional/behavioural outcome, absence of focal cases in the school-age cohort), our results suggest that a follow-up is necessary beyond the early preschool years in order to understand the long-term outcome.