The lifetime maternal caregiver strain (CS) associated with raising a child with attention-deficit/hyperactivity disorder (ADHD) into adolescence and young adulthood was examined in the Pittsburgh ADHD Longitudinal Study (PALS), a longitudinal study of individuals diagnosed with ADHD in childhood and recontacted in adolescence and young adulthood for yearly follow-up. Mothers of adolescents/young adults with (n = 364, 89.6% male; Mage = 19.79) and without childhood ADHD (n = 240, 88.8% male; Mage = 18.97) rated their lifetime maternal CS at Wave 3. Adolescent/young adult (AYA) ADHD and ODD severity measured at Wave 1, AYA delinquency measured at Wave 2, and school disciplinary actions combined from Waves 1 and 2 were explored as mediators of the association between childhood ADHD and lifetime maternal CS at Wave 3 using path analysis. AYA gender and age, parental marital status, maternal depression and ADHD, and highest parental education were included as covariates. Greater lifetime CS was reported among mothers of adolescents/young adults with versus without childhood ADHD. In the mediation model, direct effects of childhood ADHD on AYA ADHD and ODD severity, delinquency, and school discipline problems emerged, and direct effects of AYA ODD severity, delinquency, and school discipline problems on lifetime CS emerged. AYA ODD, delinquency, and school discipline mediated the association between childhood ADHD and lifetime maternal CS. These findings extend research on childhood ADHD to identify AYA sequelae contributing to maternal CS. Future research on the transaction between AYA functional impairment and maternal CS across the transition from adolescence into adulthood is needed to clarify opportunities for intervention. (PsycInfo Database Record (c) 2020 APA, all rights reserved).