Participants were 36 adolescents diagnosed with attention-deficit/hyperactivity disorder (ADHD) who completed a summer treatment program. Self-report measures included the IOWA Conners Inattention/Overactivity and Oppositional/Defiant subscales, peer and staff interaction ratings, and a daily guess if the placebo or methylphenidate was given during a double-blind medication trial. Self-reports were reliable, and some of the self-report measures distinguished between placebo and methylphenidate conditions. However, the self-report measures exhibited weak correlations with observed frequencies of negative behavior and did not make a unique contribution beyond what was reported by adults. This study replicates previous findings that adolescents may be poor sources of information about ADHD symptoms, but adolescents receiving treatment for ADHD may be able to provide valid self-reports about negative social behavior.