Attention-deficit hyperactivity disorder (ADHD) is characterized by symptoms of inattention, hyperactivity and impulsivity, and affects 3–5% of school-aged children. Recommendations regarding the relative importance of electroencephalography (EEG) in ADHD are ambiguous. Most guidelines for ADHD diagnostics only recommend an EEG in cases with clinical suggestion of seizure disorders or degenerative conditions and not for routine use. Although in most cases of ADHD, an EEG is indeed unnecessary, without a routine EEG, some children with absences or rolandic spikes will not be identified and, therefore, will not be treated correctly. The EEGs of children with ADHD demonstrated increased theta activity and fewer alpha waves compared with controls. Research on event-related potentials is helpful in identifying underlying attentional deficits in ADHD. Future studies that combine EEG analysis with functional magnetic resonance imaging data, positron emission tomography studies or genetic research will help to improve our knowledge about the pathophysiology of ADHD and perhaps lead to a better, more individual treatment in well defined subgroups.