This study dealt with the electroencephalograms (EEGs) of 176 children with attention deficit-hyperactivity disorder (ADHD). Of special interest were the patients who had in their EEG some type of spike activity (spike group), in contrast with those without such activity (control group). In the entire group, 27.8% were completely normal and an additional 18.8% had positive spikes as their only finding. Definite noncontroversial, epileptiform activity was seen in 30.1%, mainly focal (usually occipital or temporal), less often generalized, with bilaterally synchronous spike and waves complexes seen in 11 children. Extreme spindles or diffuse slow waves occurred only in the spike group (one exception in each) and slow wave abnormalities (mainly frontal or temporal), nearly always mild in degree, were seen mainly in the spike group. These different findings suggest that ADHD is a condition often with organic changes in the form of EEG abnormality, at times with epileptiform activity that could contribute to a deficit in attention or a plethora of movements.