Introduction:
Among the causes of attention deficit hyperactivity disorder (ADHD) are mentioned mainly biological conditions (genetic, biochemical and anatomical). Environmental factors also significantly affect the functioning of the individual, but are largely a consequence of the determined biologically specific reactions of a child or an adult with ADHD. Thus, early diagnosis of dysfunctions is an important precondition for undertaking appropriate actions to mitigate specific symptoms and avoid various consequences related to attention deficit and hyperactivity. In diagnosing, it is necessary to take into account the objective and subjective symptoms of disorders. Here, an interview, observation, and psychological tests are also useful. Due to the difficulties in differential diagnosis related to various types of diseases, biological research is also important. Quantitative EEG (QEEG) is particularly helpful in making a diagnosis.

Objective:
The aim of the study was analysis of the usefulness of the QEEG method in diagnosing persons with ADHD, which is also the basis for planning supportive EEG biofeedback therapy.

Material and Methods:
The research presents a case study, which includes an in-depth analysis of the QEEG results concerning five randomly selected children with ADHD.

Results:
The QEEG assessment of children with ADHD shows repeated dependencies, the presence of high amplitudes of low-frequency waves – Delta, Theta, Alpha, and low amplitudes of high-frequency waves, compared to low-frequency waves. However, similar amplitudes of high-frequency waves were found – SMR, Beta1 and Beta2, and lower amplitudes of Beta2 waves, compared to Alpha and Theta.

Conclusions:
The QEEG test is very helpful in diagnosing ADHD. This method provides important information while planning EEG biofeedback therapy and checking its effectiveness.