Background and Aims: The precise roles of screen media activity (SMA) and sleep problems in relation to child/adolescent psychopathology remain ambiguous. We investigated temporal relationships among sleep problems, SMA, and psychopathology and potential involvement of thalamus-prefrontal-cortex (PFC)-brainstem structural covariation. Methods: This study utilized data from the Adolescent Brain Cognitive Development study (n 5 4,641 ages 9-12) at baseline, Year1, and Year2 follow-up. CrossLagged Panel Models (CLPMs) investigated reciprocal predictive relationships between sleep duration/ problems, SMA, and psychopathology symptoms. A potential mediating role of baseline Thalamus-PFCbrainstem covariation on SMA-externalizing relationships was examined. Results: Participants were divided into discovery (n 5 2,359, 1,054 girls) and replication (n 5 2,282, 997 girls) sets. CLPMs showed 1) bidirectional associations between sleep duration and SMA in late childhood, with higher frequency SMA predicting shorter sleep duration (â 5
0.10 [95%CI:
0.16,
0.03], p 5 0.004) and vice versa (â 5
0.11 [95%CI:
0.18,
0.05], p < 0.001); 2) externalizing symptoms at age 10-11 predicting sleep problems (â 5 0.11 [95%CI: 0.04, 0.19], p 5 0.002), SMA (â 5 0.07 [95%CI: 0.01, 0.13], p 5 0.014), and internalizing symptoms (â 5 0.09 [95%CI: 0.05, 0.13], p < 0.001) at age 11-12; and 3) externalizing behavior at age 10-11 partially mediating the relationship between baseline thalamus-PFC-brainstem covariation and SMA at age 11-12 (indirect effect 5 0.032 [95%CI: 0.003, 0.067], p-value 5 0.030). Findings were replicable. Conclusion: We found bi-directional SMA-sleep-duration associations in late childhood. Externalizing symptoms preceded future SMA and sleep disturbances and partially mediated relationships between structural brain covariation and SMA. The findings emphasize the need for understanding individual differences and developing and implementing integrated strategies addressing both sleep concerns and screen time to mitigate potential impacts on psychopathology.  Kulcsszavak: screen media activity, addictive behaviors, Internet addiction, adolescent, insomnia, brain structural covariation