Oppositional defiant disorder (ODD) and attention-deficit/hyperactivity disorder (ADHD) are characterized by symptoms that hinder successful positive interaction with peers. The main goal of this study was to examine if the presence of symptoms of ODD and ADHD affects the relationship between positive social behavior and peer status found in 7–9-year-old children who show symptoms typical of ADHD and/or ODD. Furthermore, the possible interaction with sex was investigated. We used data collected in the first wave of The Bergen Child Study of mental health (BCS), a prospective longitudinal total population study of children's developmental and mental health. The target population consisted of children in the second to the fourth, in all public, private, and special schools in Bergen, Norway, in the fall of 2002 (N = 9430). All 79 primary schools in Bergen participated in the study. Both teacher (8809 complete cases) and parent (6253 complete cases) report were used in the analyses. ADHD and ODD scores were estimated using the Swanson Noland and Pelham rating scale version IV (SNAP-IV), and peer problems and prosocial behavior were assessed using the Strengths and Difficulties Questionnaire (SDQ). We replicated the relationship between peer problems and prosocial behavior found previously in typically developing children. Our results showed that the relationship between peer problems and prosocial behavior became weaker as the ODD symptoms increased in number and severity. For ADHD this effect was only found in the teacher report of the children. A sex effect for ODD symptoms was found only using the parent report: boys with ODD symptoms showed less prosocial behavior than girls with similar levels of ODD symptoms. Since this effect was not found using the teacher data, it may imply a situational effect (school/home) for girls with high levels of ODD. The moderator effect of ODD/ADHD was comparable for boys and girls. Our findings suggest that even if children with ADHD/ODD symptoms have the opportunity to practice their social skills in peer relationships, this is not necessarily accompanied by an increase in prosocial behavior.