Background and aims: Video games are a common form of entertainment in adolescents, which may result in gaming habits characterized by impairment to reward-related decision-making. The aim of the current study was to investigate the relationship between reward processing and symptoms of gaming addiction in adolescents. Methods: Data from three consecutive follow-up years (years 2, 3 and 4) of the Adolescent Brain Cognitive Development (ABCD) Study were analyzed (n 5 6,143, total observations 5 12,745, mean age at year-2 5 12 years). Participants completed the Video Game Addiction Questionnaire (VGAQ) at each visit. Discrete stages of reward processing were measured at the year-2 visit using the Monetary Incentive Delay task while the participant completed a functional magnetic resonance imaging (fMRI) scan. Bayesian hierarchical linear models were employed to examine the longitudinal association between reward processing in regions of interest at year-2 and VGAQ scores over time. Results: Lower activation in the bilateral caudate during the anticipation of a large reward (â 5
0.87, 95% CI:
1.68,
0.07) was associated with greater VGAQ scores over time. This implies that for each one-unit increase in brain activity in the caudate, there was an associated 0.87-point decrease in symptoms of gaming addiction as measured by the VGAQ. No association was found between reward feedback and VGAQ scores. Discussion and Conclusions: The findings suggest that abnormal reward processing in the caudate nucleus is associated with symptoms of gaming addiction in adolescents. These results provide a clearer understanding of the brain mechanisms involved in gaming addiction, which could inform future preventive and therapeutic strategies.  Kulcsszavak: gaming addiction, video games, reward processing, adolescent, longitudinal, imaging