Objective: In the present study, we created a new valid rating scale to estimate the prevalence of ADHD among school-age children in Fayoum City. Method: We conducted two consequential studies (Studies 1 and 2). In Study 1, the sample comprised 106 children. The ages of the sample participants ranged between 6 and 14 years. The purpose of that study was to validate a new Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM-5)-based ADHD rating scale. In Study 2, the sample consisted of 420 children with ages ranging from 6 to 14 years. We used the new rating scale to estimate the prevalence of ADHD. Results: The first study showed that the new rating scale for ADHD was valid. The second study revealed that the prevalence of ADHD in Fayoum City was 20.5%, with 33.8% among boys and 6.8% among girls. Conclusion: We validated a new ADHD rating scale and estimated the prevalence of ADHD in Fayoum City for the first time in Egypt.