Background <p>Screen exposure may affect cognitive function in children with attention deficit hyperactivity disorder (ADHD). We aimed to investigate the relationship between screen time and cognitive function in children with ADHD and explore other risk factors for cognitive function.</p> Methods <p>The study included 184 patients with ADHD (aged 6–16 years). Socioeconomic and demographic information was collected. We assessed the core symptoms of ADHD, intelligence quotient (IQ), cognitive function (using the Das-Naglieri cognitive assessment system [DN:CAS] Chinese version), and screen time per day. Multiple linear regression was used to evaluate the factors associated with DN:CAS subscales.</p> Results <p>A higher full IQ (<i>p </i>&lt; 0.001), shorter screen time per day (<i>p </i>&lt; 0.001), and higher maternal education level (<i>p </i>= 0.029) were predictors of better scores on the DN:CAS full scale.</p> Conclusion <p>IQ, screen time, and maternal education are predictors of cognitive function in children and adolescents with ADHD. Hence, parents should understand the importance of controlling their children’s screen time to enhance their cognitive function.</p> Impact <p><UnorderedList Mark="Bullet"> <ItemContent> <p>IQ, screen time, and maternal education are predictors of cognitive function in children and adolescents with ADHD. Thus, parents should understand the importance of controlling their children’s screen time to enhance their cognitive function.</p> </ItemContent> <ItemContent> <p>Our application of DN:CAS as a cognitive assessment tool is advantageous compared to the Wechsler intelligence test. The DN:CAS Chinese version is a theory-driven assessment kit, developed based on the PASS (planning, attention, simultaneous, and successive) theory assessing cognitive function. The PASS theory is an example of a terminal cognitive processing theory based on the view of functional regions of brain operation and cognitive psychology.</p> </ItemContent> </UnorderedList></p>