Attention Deficit Hyperactivity Disorder (ADHD) is characterized by a developmental disorder involving inappropriate poor attention span or age-inappropriate features of hyperactivity and impulsivity and/or both. In order to assess the prevalence of children with ADHD in Tehran, a sample of 2667 children including both boys & girls aged between 7-12 years were selected by a 2-stage method sampling among a grid of sectors of 19 different educational areas by stratified random sampling. We tested the rate of ADHD in the considered children based on two questionnaires of Conners Parent and Teacher Rating Scales (CPRS and CTRS) and semi-structured interviews. According to the recent studies, it is possible to describe the rate of ADHD prevalence based on the CPRS and CTRS questionnaires and semi structured interview among the primary school children in Tehran (aged between 7-12 years of age) with a range of 3% to 6%. These mentioned findings are somewhat similar to the announced statistics of the American Psychiatric Association (APA)(2003).