Objective: To investigate behavioral distinctions between children with reading disabilities (RD) and attention-deficit hyperactivity disorder (ADHD). Method: A four-group mixed design consisting of children with reading disabilities only (RD only), reading disabilities and ADHD (RD/ADHD), ADHD only, and a comparison group was used. Differences between parent reports, from age 5 to 15 years, and teacher reports, from age 5 to 13 years, were examined on measures of hyperactive and antisocial behaviors. Results: The analyses indicated that, at home, children from the ADHD only and RD/ADHD groups exhibited significantly more hyperactive behaviors than children from the RD only and comparison groups. At school, children from the RD only, ADHD only, and RD/ADHD groups typically exhibited significantly more hyperactive and antisocial behaviors than children from the comparison group. With regard to antisocial behaviors, children from the RD/ADHD group exhibited significantly more antisocial behaviors than children from any other group. Conclusions: The results of the study indicate that children from these groups may exhibit either a ''pervasive'' or ''situational'' presentation of behavioral problems, a finding which suggests that in conducting an evaluation of ADHD it is important to obtain both parent and teacher reports of problem behaviors.