This article will review the use of electroencephalographic (EEG) data in children with Attention Deficit/Hyperactivity Disorder (ADHD) or symptoms indicative of ADHD, both in research directed at determining the pathophysiology of ADHD, as well as research attempting to use the EEG as a diagnostic tool. In addition, we briefly review concepts important in quantitative analysis of EEG data. Overall, although some studies show enhancement of certain frequency bands relative to others within groups of ADHD children compared to normal controls, to date neither traditional nor quantitative EEG has revealed pervasive or consistent patterns of EEG abnormalities with sufficient specificity or sensitivity to separate children with ADHD from normal subjects. An exciting and promising recent development in this area of research involves advanced quantitative EEG analysis that has revealed an index shown, in small preliminary studies, to clearly and reliably differentiate ADHD from non-ADHD males. The use of EEG as a diagnostic tool for ADHD warrants further study, including additional large studies to help determine and clarify the specificity and sensitivity of the multiple EEG measures in differentiating ADHD and its subtypes from non-ADHD and other medical and psychiatric disorders.