BACKGROUND: Physical activity has been documented to influence several aspects of physical and mental health. Growing evidence shows that physical activity can improve attention. Less is known about how symptoms of inattention and hyperactivity / impulsivity in childhood are associated with physical activity in adolescence. We aimed to explore this relationship further. METHODS: We used a cohort of 3949 Swedish children (1884 boys and 2065 girls) with data collected at ages 9 (or 12) and 15. We investigated the influence of symptoms of inattention and hyperactivity / impulsivity in childhood - age 9/12 (inattention and hyperactivity/impulsivity separately) on self-rated physical activity at age 15, using multiple logistic regression models. We considered potential confounders such as sex, parental education level, physical activity in childhood and neurodevelopmental comorbidity. A cluster robust sandwich estimator was applied to adjust the standard errors for the nested twin data when computing the regression models. RESULTS: Symptoms of inattention in childhood (9/12) predicted less physical activity in adolescence (age 15) (OR = 0.83 CI = 0.78-0.89), whereas the opposite was true for hyperactivity/impulsivity (OR = 1.08 CI = 1.02-1.10). These associations still remained when taking possible confounders into account including neurodevelopmental and neurodevelopmental related comorbidity. CONCLUSIONS: These findings support the importance of helping children and adolescents with inattention symptoms to engage in physical activity in suitable settings.