["Journal of Child Psychology and Psychiatry, EarlyView. ", "\n\nBackground\nExecutive functioning (EF) challenges are common among autistic youth and persist throughout childhood and adolescence; they have been linked to important outcomes, including poorer mental health, adaptive skills, and overall quality of life. Despite the significance of EF in autism, few studies have examined the trajectory of EF challenges longitudinally, and those that have are constrained by small sample sizes, limited age ranges, and a focus on global EF at the expense of specific EF subdomains.\n\n\nMethods\nThis study examines the trajectory of parent‐reported EF flexibility, working memory, and inhibition challenges in autistic youth from early childhood to young adulthood and their relationship to parent‐reported aggression, anxiety, and depression symptoms. Leveraging a longitudinal sample of 313 participants (age range = 2–25, 79 females, mean age at first visit = 9.5 ± 4.6 years, age range at first visit 2.6–23.1 years; mean FSIQ = 103.3, FSIQ range 52–159; mean number of visits per participant = 2.3, range 2–9) across 941 observations, multilevel growth curve modeling was used to examine the trajectory of EF challenges and their relationship to mental health across time.\n\n\nResults\nWe found that EF challenges persist in autistic people from 2 to 25 years old, regardless of cognitive ability and parent education level. Although symptoms of aggression decline with age, depression symptoms increase with age in this sample of autistic people. Notably, autistic females are at unique risk for increasing anxiety in adolescence. Flexibility challenges in particular predict mental health outcomes across anxiety, depression, and aggression symptoms.\n\n\nConclusions\nThese data demonstrate the enduring nature of EF challenges among autistic people during childhood and into young adulthood, as well as their influence on mental health. EF and flexibility, in particular, are potent and persistent yet malleable predictors of key outcomes, making them important targets for intervention.\n\n"]