Given that attention-deficit/hyperactivity disorder (ADHD) and obesity are 2 frequent conditions that co-occur, which has implications for the management of both conditions, experts aspired to explore whether ADHD symptoms predict BMI and vice versa from late childhood (10–12 years) up to early adulthood (20–22 years). Participants were adolescents from the Tracking Adolescents’ Individual Lives Survey cohort in the Netherlands (n = 2773, 52.5% male, mean age = 11 years at baseline, 5 waves up to mean age 22).