The aim of this study was to investigate the relationships among childhood trauma, dissociative experiences, and internet gaming disorder (IGD) in young adults diagnosed with attention deficit hyperactivity disorder (ADHD) and age- and gender-matched controls. Forty participants diagnosed with ADHD at a university hospital psychiatric outpatient clinic and 40 healthy controls completed a test battery that included a sociodemographic form as well as the Adult ADHD Severity Rating Scale (ASRS), Childhood Trauma Questionnaire (CTQ), Dissociative Experiences Scale (DES), Somatoform Dissociation Questionnaire (SDQ), and Internet Gaming Disorder Scale–Short Form (IGDS9-SF). The CTQ (t = −4.61, p < .01), DES (t = −4.71, p < .01), SDQ (t = −2.40, p < .01), and IGDS9-SF (t = −4.89, p < .01) scores were significantly higher in the ADHD group than in the control group. A hierarchical regression analysis that explained 50% of unique variance in internet gaming disorder (IGD) indicated that being male (β = 0.41, t = 4.61, p < .001) and having an ADHD diagnosis (β = 0.48, t = 5.49, p < .001) are robust predictors. Additionally, the DES score, which indicates the severity of psychoform dissociation (β = 0.34, t = 2.43, p = .017), was found to be significantly associated with IGD after controlling for ADHD diagnosis and childhood trauma. While excessive gaming may increase dissociative symptoms, the mental state of dissociative experiences may be a predisposing factor for IGD; however, further studies are needed to investigate these claims.