We investigated a group of children aged 9-12 years with attention deficit hyperactivity disorder (ADHD) combined type, have divided into two variants of the clinical picture of ADHD: residual-organic variant (ADH D RO) and idiopathic variant (ADHD RI). We studied the power spectral analysis in the main frequency bands in background EEG eyes closed and are open. The significant differences between both groups observed in the theta frequency band in the fronto-central and occipital leads. In the fronto-central leads of the cortex were the maximum values in the group of children ADHD RO, whereas in children with ADHD IR, the largest values of power spectra were in the occipital leads. Statistically significant differences in spectral power in the alpha range between healthy subjects and groups children with ADHD had not been received. Thus, our studies have shown that these two variants of ADHD have some neurophysiological differences that must be considered when choosing a treatment.