Objective: Children with attention deficit hyperactivity disorder (ADHD) who participated in a randomized clinical trial, which compared a brief intensive multimodal behaviour therapy combined with optimally titrated methylphenidate to optimally titrated methylphenidate alone (n=45), were re-assessed at adolescence in a naturalistic follow-up 4.5 to 7.5years after treatment. Also a matched normal control group was recruited (n=23). Methods: Assessments at follow-up included diagnostic status, ADHD symptoms, oppositional and conduct behaviour, substance abuse symptoms and parenting stress. Results: Of the 24 adolescents participating in the follow-up study, 50% still met diagnostic criteria for ADHD. There were no significant differences between adolescents at follow-up and those lost for follow-up. At follow-up, adolescents in the combined treatment condition used significantly less medication than children in the methylphenidate condition; there were no other significant differences between the treatment conditions. The adolescents showed a significant decline in hyperactivity/impulsivity, oppositional and conduct disorder symptoms from post-test to follow-up. Only inattention symptoms increased from post-test to follow-up but not to pre-test levels. The adolescents originally diagnosed with ADHD fared significantly worse than the matched controls on all outcomes, except on conduct disorder and substance abuse symptoms. Conclusions: Our study shows in adolescents, diagnosed with ADHD in childhood, age-dependent decline of ADHD symptoms, although they still fared significantly worse than matched normal controls. Implications of results are restricted by small samples size, and the results may be subject to chance findings and need replication before firm conclusions can be drawn. © 2011 John Wiley & Sons, Ltd.