Background: Attention-deficit hyperactivity disorder (ADHD) is the name of a group of behaviors found in many children and adults. Children with ADHD have trouble paying attention in school or at home. Children may be much more active and/or impulsive than what is usual for their age; these behaviors contribute to significant problems in relationships, learning and behavior. Aim of the work: The study aimed to assess knowledge and attitude of teachers toward (ADHD). Subjects and Methods: The study was descriptive cross sectional research design; it was conducted in ten public primary schools at Assiut city which selected randomly and the sample size was (360). Three tools used in the present study, the first tool include personal characteristics of the participants, the second tool Knowledge of Attention Deficit Disorder Scale (KADDS) to measure teachers’ knowledge and perceptions about ADHD and the last tool teachers' attitudes scale toward children with ADHD to assess teachers’ beliefs and attitudes toward ADHD. Results: The main findings of the study were more than two fifth (42.2%) of teachers had pervious dealing with ADHD and more than three quarters (76.1%) of them had unsatisfactory level of knowledge; while more than half (55.0%) of teachers had positive attitude toward ADHD. Also there was statistical significant correlation (r=0.249 & P= 0.000*) between total score of teachers' knowledge and attitude toward ADHD. Conclusion: The present study concluded that the teachers had poor knowledge while attitude of them were positive. Recommendation: The study recommended that teachers' knowledge must be improved by implementing the educational program about ADHD.