OBJECTIVE To determine whether childhood attention-deficit hyperactivity disorder (ADHD) and persistence of the disorder are associated with later difficulty in adolescent peer relations. METHODS One hundred eleven children with ADHD were interviewed as adolescents and compared with 100 adolescents without an ADHD history (aged 13-18 years). The multi-informant assessment strategy included parents, teachers, and adolescents. RESULTS Parents of probands reported fewer close friendships and greater peer rejection compared with the non-ADHD group. Probands reported that their friends were less involved in conventional activities compared with the non-ADHD group. Childhood aggression predicted less self-perceived social competence for probands. The long-term effects of ADHD on social functioning were more pronounced for probands with persistent ADHD or conduct disorder in adolescence. CONCLUSIONS Impairments in peer relations for ADHD youths, known to be common in childhood, also exist in adolescence. Given the developmental significance of peer relations, further research into the causes and treatment of poor social functioning in youths with ADHD is recommended.