Background and aims: Adolescent problematic gaming is a global public health issue, and is associated with numerous negative outcomes. The Big Two personality traits, neuroticism and extraversion, have been identified as significant predictors of problematic gaming in adolescents. However, most previous studies have been cross-sectional, limiting the ability to explore their mutual influences or causality inference. This study addresses this gap by employing a longitudinal design and utilizing the Random Intercept Cross-Lagged Panel Model (RI-CLPM) to examine the bidirectional relations between the Big Two personality traits and problematic gaming at the within-person level. Methods: This study included 3,307 students (Mean age 5 11.30, SD 5 0.48, 43.6% being girls). Participants were assessed annually, completing a total of four assessments over the course of the study. Results: The RI-CLPM analyses revealed that neuroticism and problematic gaming significantly predict each other. Extraversion acts as a protective factor against adolescent problematic gaming, whereas problematic gaming leads to a decrease in extraversion levels. Additionally, the longitudinal relations between neuroticism and problematic gaming exhibit significant sex differences. Discussion and conclusions: This study provides insights into the interplay between the Big Two personality traits and problematic gaming in adolescents. These findings emphasize the need for prevention and intervention strategies that address personality traits as risk factors while recognizing how problematic gaming can influence personality, promoting a more holistic approach. The observed sex differences highlight the importance of integrating sex-specific considerations in interventions.  Kulcsszavak: neuroticism, extraversion, problematic gaming, Random Intercept Cross-Lagged Panel Model