Background: Research has demonstrated that childhood maltreatment is a significant predictor of problematic internet game use in adolescents. However, the underlying mechanisms of this relation, particularly the mediating processes and gene-environment interactions (G3E), remain insufficiently understood. This study employed a multi-informant, longitudinal design within a G3E framework to examine the mediating role of internalizing symptoms in the relation between childhood maltreatment and problematic internet game use. Additionally, it investigated whether FKBP5 gene variation moderates these associations. Methods: A total of 1,592 third- to fifth-grade students (42.2% girls; Mage 5 10.42 years, SD 5 0.94) and their parents participated in a three-wave study conducted at six-month intervals. Results: Findings indicated that both emotional abuse and neglect each significantly predicted problematic internet game use, with internalizing symptoms mediating both relations. Moreover, higher FKBP5-related cumulative genetic scores amplified the impact of emotional abuse on internalizing symptoms, which, in turn, exacerbated problematic internet game use. Conclusion: The results underscore the importance of considering both genetic and environmental factors in understanding the development of problematic internet game use. Interventions should focus on mitigating the emotional consequences of childhood maltreatment and accommodating genetic predispositions to stress, thereby providing a more comprehensive approach to preventing and treating problematic internet game use in adolescents.  Kulcsszavak: childhood maltreatment, problematic internet game use, internalizing symptoms, FKBP5 gene variants