AimThis study examined factors associated with severity, incidence and/or persistence of internet gaming disorder (IGD) in children and adolescents. Design, Setting, Participants Prospective cohort study with 2-year follow-up study in South Korea. A total of 2319 3rd-, 4th-and 7th-graders enrolled into the internet user cohort for unbiased recognition of gaming disorder in early adolescence [internet user Cohort for Unbiased Recognition of gaming disorder in Early adolescence (iCURE)] and analyzed for the current study. Measurements Severity of the IGD features was assessed by the Internet Game Use-Elicited Symptom Screen (IGUESS), a self-reported questionnaire based on the DSM-5 IGD criteria. Participants with IGUESS scores ≥ 10 were considered to be at high risk for IGD (HIGD). Time spent playing on-line games, game types, depressive symptoms, trait anxiety, attention deficit hyperactivity disorder (ADHD) symptoms, social support, openness of communication with parents, attachment to parents and potential confounders were assessed by self-report.Findings A total of 175 (7.5%) students were classified as HIGD cases upon initial assessment. The independent risk factors of incidence of HIGD included playing on-line games for ≥ 240 minutes/day, playing multi-player games, depressive symptoms and ADHD symptoms [adjusted rate ratios (aRRs) = 2.03, 1.63, 2.04, 2.53, respectively; all P < 0.05]. Factors related to changing IGD severity scores were playing on-line games for 60-239 minutes/day, playing single-player on-line games, higher attachment and social support [adjusted incidence rate ratio (aIRRs) = 1.38, 1.22, 0.86, 0.87, respectively; all P < 0.05]. Independent predictors of persistence of HIGD were playing on-line games for ≥ 240 minutes/day and ADHD symptoms (aRRs = 2.63, 2.14, respectively; all P < 0.05). Conclusions Among adolescents in South Korea, the existence of ADHD symptoms and spending more than 4 hours per day playing on-line games were associated with the occurrence or persistence of high risk for internet gaming disorder.