This study aims to assess the mediating effect of childhood trauma and dissociative experiences on the relationship between self-reported ADHD symptoms during childhood and adulthood in two separate cross-sectional studies. In Study 1, undergraduate students completed an online survey including a sociodemographic form, the Adult ADHD Self-Report Scale (ASRS), the Wender Utah Rating Scale (WURS), the Childhood Trauma Questionnaire (CTQ), and the Dissociative Experiences Scale (DES). Data from 1,148 participants were analyzed using descriptive statistics and mediation analysis. In Study 2, sociodemographic, clinical, and diagnostic data from 202 adults with ADHD, followed at the Adult Neurodevelopmental Disorders Clinic at Selçuk University, were analyzed. Diagnostic evaluations were conducted using the Structured Clinical Interview for DSM-5 Clinician Version. Clinical data included age, gender, years of education, comorbid conditions, and current ADHD medication use. The same self-report scales (ASRS, WURS, CTQ, and DES) were administered in both studies. The two samples differed significantly in terms of clinical characteristics and self-reported symptoms. Current ADHD symptoms were not only directly associated with childhood ADHD symptoms but also indirectly associated with them through increased childhood trauma and dissociative experiences, independent of demographic and clinical confounding factors in both studies. The pathway involving childhood trauma and dissociation may partially mediate the persistence of ADHD symptoms from childhood to adulthood in both undergraduate and adult ADHD samples. Longitudinal clinical studies are needed to better understand how the childhood trauma and dissociation pathway may influence the persistence of ADHD symptoms as individuals age, potentially extending into adulthood.