The aim of this study was to analyze age-dependent differences in attentional performance in subjects aged 8-16 years with attention deficit/hyperactivity disorder (ADHD) with or without disruptive behavior disorders (DBD). Age effects were investigated in three different groups (ADHD [N = 118], ADHD + DBD [N = 105], and controls [N = 105]) on a sustained attention and a Go-No-Go paradigm. Attentional competencies increased with age and children in the two clinical groups performed worse than control children on both tasks. However, these group differences between ADHD, ADHD + DBD, and controls decreased with increasing age. Thus, age-related differences must be considered in neuropsychological studies.